No matter your reasons for wanting to grow your own tomatoes, be it for their health benefits, food security, to preserve by drying, making sauces, pastes or jams, or simply to save money, knowing what nasty pests and diseases could possibly devastate your crop, and how to spray to help prevent them from even starting, will go a long way to ensuring that your tomatoes remain healthy and produce well all season long.
Tomatoes are susceptible to fungal diseases like blight, and pests like whitefly, red spider and leaf miner, to name a few, and all these will affect their yield. However, if you are prepared in advance you can get on top of any problems before they destroy your plants.
There is nothing worse that growing and caring for your tomato plants, and just as they start to produce well they become afflicted with blight or weakened by various pests, and your plants start deteriorating slowly, no matter how much you spray. It’s enough to put one off vegetable gardening forever! So, if you want to grow tomatoes successfully be prepared to spray on a regular basis, as they say “prevention is better than cure”, and this is especially true when it comes to diseases like blight.
To grow tomatoes successfully you will definitely need to invest in a good commercial fungicide that prevents early blight, and you may also need at least one pesticide to treat the most devastating and difficult to control tomato pests, like red spider and whitefly, and if tomato leaf miner is a problem in your region, you will definitely need to purchase a good product that covers this.
Often new gardeners will bemoan the cost of purchasing fungicides and pesticides at first, believing that the cost of these will outweigh the savings they were expecting by growing their own. But think of it this way, for the average household these sprays will last for a couple of seasons and they can also be used on many other ornamental plants, fruit and vegetable crops, not just tomatoes.
Many of the other common garden pests like aphids can easily be controlled with remedies made at home. There are hundreds of DIY recipes online to treat tomato pests and diseases, using common household ingredients and herbal sprays. So, if you are that way inclined, you can search for the recipes you feel would be the most effective and easiest for you to make at home.
Before we discuss some of more serious pests and diseases that can affect tomatoes and the many good sprays available commercially to prevent and control them, not forgetting the DIY sprays, let’s talk about some common sense preventative measures you can take to keep your tomatoes happy.
Getting the growing basics right certainly makes a huge difference in the health of tomatoes, and this includes ensuring that your tomatoes receive sufficient sun, the soil is fertile and drains well, regular feeding and watering, and crop rotation, are all vital, and will go a long way in keeping tomato plants healthy and happy. Members can click here to read my full article on growing tomatoes, including good companion plants to grow with them.
It is also vital that there is a good flow of air between the leaves and stems of tomatoes, so space the plants correctly, and ensure they are staked in a way that maximizes air flow. Keep watch over your tomatoes and pluck off any leaves that show signs of disease immediately and burn them, or throw them into the garbage.
When moisture remains on the leaves for long periods, and especially at night, it creates a perfect microclimate for the spores of fungal diseases to establish, so try to keep the leaves of your tomato plants dry. Drip irrigation or watering at the base of the plant can help prevent this, and if you use an overhead sprinkler system or similar method to water your tomatoes, do so in the morning as this allows time for the plants to dry out quickly and thoroughly. Mulching the roots of the plant with washed river sand, straw, or bark chips will prevent ‘water splashback’ which transfers fungal spores from the soil onto the leaves and helps diseases fester.
Maintaining good garden hygiene will also go a long way in preventing fungal outbreaks, so keep your vegetable garden clean, as fungal spores can overwinter on plants left in the garden from the previous year.
A three to four year crop rotation programme with non-related crops is recommended to reduce the build-up of soil-borne pests and diseases. If you don’t have space for crop rotation, or if your soil is contaminated, plant tomatoes into large grow bags or containers which can be sterilised and filled with fresh soil each season.
Practice companion planting to deter pests and keep inspecting your plants regularly to catch any infections or infestations early.
Leaf Spot and Early Blight
Septoria Leaf Spot
Septoria Leaf Spot typically appears early in the season and first shows on the plant’s lower leaves as small, circular brown spots, that often have yellow halos around them. It doesn’t negatively impact the fruit but needs to be dealt with all the same.
Click here to see Google images of Septoria Leaf Spot
Early Blight
Early blight is the most common and devastating disease of tomatoes, and adverse summer weather conditions play a role in the development of fungal diseases, which are triggered by rainy weather and cool nights, high humidity, or heavy dew. Remember that when it comes to fungal diseases like early blight on tomatoes, prevention is better than cure, and you need to have the spray on the leaves to prevent a breakout. Preventative spraying should start early in the season and continue throughout, until harvesting is over.
Early blight can appear at any time but usually rears its ugly head mid-season and can set in the stems and leaves of tomatoes, and is identified by legions with target-like rings. These dark, non-uniform spots start on the lower leaves, which quickly turn yellow and die. Early blight will eventually damage the fruit. This fungal disease loves tomatoes and other nightshade plants such as peppers, eggplants, and potatoes. Unfortunately, blight rapidly spreads throughout the plant to neighbouring ones as well.
Click here to see Google images of Early Blight on tomatoes.
Late Blight
Late Blight is the least common and most destructive form of blight, and although it can appear at any time, it often appears late in the growing season and affects large portions of the leaves, turning their undersides white and fuzzy, and destroying crops extremely fast. Affected plants should be removed immediately and burnt.
Click here to see Google images of Late Blight on tomatoes.
Fungicides to prevent leaf spot and early blight
There are many very good products available to the gardener today, and you need to do your own research and purchase what you prefer to use. In some towns the products mentioned below may not be available at garden centres, however they are all available online at good prices.
Biogrow ‘Copper Soap’
An excellent organic fungicide to prevent leaf spot and early blight is Biogrow ‘Copper Soap’, with the active ingredient Copper Octanoate. This product is a patented, fixed copper fungicide, made by combining a soluble copper fertiliser with a naturally occurring fatty acid. The copper and the fatty acid combine to form a copper salt of the fatty acid, known technically as soap. Copper soap fungicide controls many common diseases using low concentrations of copper, down as low as 90ppm. The net result is an excellent vegetable, fruit and ornamental fungicide. It decomposes to form soluble copper, and fatty acid, both of which can be used by microbes and plants.
This product controls diseases on a wide range of plants, including many vegetables, fruits and ornamentals. As with most fungicides it acts to protect plants from infection. Therefore, it is important to have the copper soap on the leaf, flower or fruit before the pathogen is able to cause an infection. This product will control fungal diseases such as: blight on potatoes and tomatoes, powdery mildew and downy mildew on grapes, vegetables and ornamentals, and rust.
Margret Roberts ‘Organic Fungicide’
Margret Roberts ‘Organic Fungicide’ is another excellent preventative product using organic plant acids for powdery and downy mildew, bacterial leaf spot, early blight and damping off. Plant acids weaken fungus cell walls making them susceptible to other forms of control. Leaf cells can absorb the organic acids and use them in beneficial processes. It can be used on food crops, ornamentals, herbs, and roses. This product has a low impact on other beneficial predatory insects. It does not affect fish, birds, humans, or household pets like cats and dogs.
Make this easy DIY organic spray to help prevent blight in the garden, or search for your favourite recipe online.
3 tablespoons of bicarbonate of soda, 1 tablespoon of vegetable oil, 1 teaspoon of dish soap, 4 litres of water. Mix all the ingredients together and spray. As a preventative spray you will need to reapply the mixture at least once a week, and more often during rainy weather, and spray early in the morning or late in the day when the sun isn’t so intense. Already infected plants are difficult to cure but you can continue to spray regularly, including the surrounding plants, as the infection can spread quickly to other crops.
This recipe can also be used to organically control powdery mildew, on vegetables like egg plants and pumpkins during long stretches of humid weather!
Now for those pesky insect pests:
Tomatoes are targeted by a wide range of pests, and infestations will vary from place to place, and from season to season, but some form of pest control will invariably be necessary. The most common tomato pests in South Africa are root-knot nematode, cutworm, bollworm, army worm, leaf miner, thrips, red spider mite and aphids. I have not covered all of them below as it would make this article far too long.
Early detection is the key to pest management, so look out for any nasty visitors, and start to spray before the infestation becomes overwhelming and difficult to manage; this is especially true for whitefly and red spider.
In some towns the products mentioned below may not be available at garden centres, however they are all available online at good prices.
Whitefly
When it comes to pests whitefly is one of the most common and most damaging to plants, and you’ll often start to see them in mid- to late-summer when it gets warm and humid. Their populations can explode quickly and cause serious infestations, and whiteflies can be tough to eliminate, so it’s important to recognize the early signs of infestation and apply the necessary treatment to get them under control. Whitefly is a major pest that targets tomatoes and they also spread viruses and suck the plant sap which deforms and stunts the plant, affecting yields. Other food crops most affected include beans, brassicas, cucumber, eggplant, grape, okra, peppers, potatoes, squash, and tomatoes.
Despite its name, whitefly is not a true fly, but is closely related to aphids, mealybugs, and scale. These soft-bodied winged insects are moth-like in appearance, and are most often grey-white in colour. Because of their tiny size, they can be hard to spot. Noticing tiny, white insects on your plants that fly off the leaves if disturbed, and clusters of eggs underneath the leaves, is a sure sign of whitefly.
In warmer regions, whiteflies are capable of overwintering and reproducing outdoors throughout the year, so they can be a problem for both indoor and outdoor plants. With heavy infestations the plant will quickly become extremely weak and may be unable to carry out photosynthesis. The leaves will wilt, turn pale or yellow, growth will be stunted, and eventually leaves may shrivel and drop off the plant.
When spraying for white fly, be sure to cover the entire plant, drenching the underside of the leaves where the pests rest, and keep up the spraying programme as recommended on your product for at least 21 days, because that is the length of the life cycle of adult whiteflies.
Click here to see Google images of whitefly
Red Spider Mites
There are many different species of mites, which attack our plants, but it is the common red spider mite and the two-spotted mite that are the most common. Red spider mite populations can explode during hot, dry weather, and they lay their eggs on the undersides of the leaves where it is relatively dry, and are so minute that most people don't even see them. Signs of infestation are fine white spider webs on the plant, a mottled, silvery look to the top of the leaf, or a severe yellowing or bronze colour to the leaves, leaves dropping off, and leaf curl.
The life cycle of red spider mites involves the laying of eggs, followed by 4 active life stages: larval, two nymph stages and adults, with a resting period between each of the active life stages. The full life cycle can be completed in 14 days at temperatures of 25°C and above. In cold climates, tomato red spider mite overwinters as eggs or adult females in the nooks and crannies of tree bark and plant stems, and in leaf litter or the upper soil layer at the base of host plants. In tropical and subtropical areas they may remain active year-round. It is most important to spray as directed on the bottle in order to break their breeding cycle.
Click here to see Google images of red spider
Insecticides and methods for controlling red spider mites and whitefly on tomatoes
Regular plant inspection helps to control a red spider mite or white fly infestation before it gets out of hand, so check the undersides of your plants leaves often, you will soon learn to spot them. Spider mites and white fly seem to miraculously appear during hot and dry summer spells, and shelter in the little microclimate created underneath the leaves of plants. If you spot them early, first cut off and dispose of the worst infected leaves, then drench the entire plant, but especially the undersides of the leaves, using a strong stream of water from a hose pipe. If done regularly during hot and dry weather this will go a long way in controlling these pests. And, if their shower is followed by an insecticidal spray this is the most effective. Do this early on a dry day so the leaves and stems of your tomatoes have sufficient time to dry out totally before nightfall. Doing this regularly during this type of summer weather, can keep mites and white flies at bay.
Biogrow ‘Bioneem’
Biogrow ‘Bioneem’ comes from the Neem tree and is a great choice for gardeners because it is used to control a wide range of insects, (up to 200 types) including our main terrorists of tomatoes: white fly, red spider mites, and leaf-miners. It also does mealybugs, thrips, fruit flies, leaf hopper, weevils, and many, many more gogga’s.
The key insecticidal ingredient found in the neem tree is Azadirachtin, a naturally occurring substance. It blocks the insect’s production and release of vital hormones rendering them unable to moult, thus breaking their life cycle. Depending on the stage of life-cycle, insect death may not occur for several days. Azadirachtin acts as a feeding deterrent for some insects, but for those who do take a nibble, if only minute quantities are ingested the insects stop feeding. Residual insecticidal activity is evident for up to seven days or longer, depending on insects and application rate.
Because neem products must be ingested to be effective, they are relatively harmless to insects that pollinate crops and trees, such as butterflies, spiders and bees, as well as our beloved lady bird bugs that consume aphids and are a welcome sight in the garden, and not forgetting the beneficial wasps that control various crop pests. Therefore only insects that feed on plant tissue succumb, while those that feed on nectar or other insects rarely contact significant concentrations of neem products. I would advise trying to avoid spraying directly into blossoms, if possible, and to spray when pollinators are not that active. Also, do not apply in temperatures above 30°C, as Bioneem is an emulsifiable concentrate.
Biogrow ‘Vegol'
Biogrow ‘Vegol’ will control white fly and mites on tomatoes. It is 96% Canola Oil and is a contact insecticide with ovicidal activity that can be used in both the dormant and growing seasons, and does not persist in the environment. It is a proprietary formulation consisting of pure canola as active ingredient that kills all stages of insects. This product will also control aphids, mealy bugs, leafhoppers, scale, immature plant bugs, sawfly larvae, psyllids, leaf beetle larvae and phylloxera.
For use indoors, outdoors and in greenhouses, on fruit and nut trees (e.g., apples, cherries, peaches, pears, nuts); flowering, foliage and bedding plants; corn; soybean; melons; tomatoes; vegetables (e.g., beans, cabbage, cucurbits, peas, potatoes); figs; small fruits (e.g., grapes, strawberry, raspberry); citrus; ornamental and shade trees (e.g., birch, evergreens, holly, oak); and houseplants. Remember to spray the entire plant and especially the undersides of the leaves.
DIY recipes for red spider mites and whitefly
There are hundreds of easy DIY organic sprays online to help prevent and control spider mites and whiteflies naturally, so find those that suit your needs best, or just use what you have on hand.
Cayenne pepper or hot chilli pepper spray for red spider mites:
Sprays using the hottest chillies you can find will keep a host of chewing insects away from your plants, including beetles like the brown ones we call “Christmas beetles”. Just remember to wash your veggies well before serving, or your family may just get a hot surprise!
Take one teaspoon of very hot cayenne pepper or the hottest chilli you can find, chop or blend and steep for about an hour in one cup of hot water. Once cool, strain, add a drop of dishwashing liquid, and spray undiluted. As a deterrent, spray once a week, but if your plants are already infested, spray every few days, and after any rainfall.
Garlic insecticide and fungicide spray:
Garlic spray works well for red spider mites and also deters many other garden pests like aphids and slugs. It can also help to eliminate powdery mildew.
Peel the cloves from a whole head of garlic and put in a food processor or blender with 250ml of warm water and purée the mixture. Alternatively, chop or crush the cloves as finely as you can by hand and mix well, using hot water.
Add a further 700ml of water to the mixture, along with 30ml of any liquid soap. Blend again and then transfer to a clean jar. Allow the mixture to steep for about 24 hours, or at least 12 hours, so the garlic can infuse the liquid with its potent sulphur compounds.
Strain through a muslin cloth or fine mesh strainer to prevent clogging the nozzle on your spray bottle. Pour the liquid into a container, seal and store in the fridge between uses.
Use undiluted and spray the plants thoroughly, covering both sides of the leaves with an even coating of the spray. As a deterrent, spray once a week, but if your plants are already infested, spray every few days, and after any rainfall.
Now, this is how my mind works – why not combine very hot chillies and garlic together, utilising both their powers in one spray – it’s like using a two-in-one shampoo, but only for tomatoes. And, yes it really works well!
DIY canola oil recipe for red spider mites:
Canola oil is very good in controlling spider mites if sprayed diligently twice a week. Mix canola oil with water. Dilute the oil according to the severity of the infection. For plants with severe spider mite infestation, you can use a 2% solution.
Essential oils as insecticides:
This as a truly fascinating subject, and essential oils are used to deter a vast array of garden pests, so if you already have some in your medicine cabinet, chances are you can use them on your plants too. All you have to do is to add them to water and spray – simple. There are so many recipes online, I will leave it up to you to find those that you think would serve you best, but here are some good ideas to get you started.
There are no hard and fast rules on dosage strength, and in organic gardening, oils with a very sharp scent like eucalyptus, lemon oil, cinnamon oil, or rosemary oil, are used more sparingly than those with a gentler aroma like chamomile.
Cinnamon oil must be one of the very best non-toxic and non-hazardous pesticides, and its efficacy to kill spider mites has been proven numerous times. And, because this oil targets adult spider mites as well as the eggs, it provides very effective long-term protection, so add about 4 drops to 1L water in a spray bottle, and agitate the bottle as you spray. If you are spraying plants with glossy leaves you can add a drop of dishwashing soap.
Lemon oil is one of the most popular choices for preventing spider mites, perhaps because it smells so wonderful. Lemons are known for being natural antibiotics and have strong antimicrobial properties, so add about 4 drops to 1L water in a spray bottle, and agitate the bottle as you spray. If you are spraying plants with glossy leaves you can add a drop of dishwashing soap.
Spider mites absolutely hate the strong smell of menthol too, and many gardeners claim eucalyptus oil works like magic. The ‘magic’ is also due to its antibacterial and bactericidal properties. Because this oil is very pungent, use only 2 to 3 drops in 1L of water.
I encourage you to do some research online about this subject. It’s fascinating how essential oils benefit both humans and plants. They are safe and effective, and because only small doses are used, your oils should last a long time. It also wonderful to just add a couple of drops to water, and off you go - no worries about poisoning yourself in the process.
Tomato Leaf Miner
The tomato leaf miner (Tuta absoluta), is an insect indigenous to Peru and widespread in other South American countries. It migrated from South America to Europe, and from there it spread throughout Africa. In South Africa it was first detected in in the eastern parts of Mpumalanga in 2016, and is now a notifiable pest, meaning the Department of Agriculture, Forestry and Fisheries (DAFF) must be informed of its presence.
The eggs of the tomato leaf miner are laid by adult moths that are about 10mm long, with silvery-grey scales, and long, filiform banded antennae. These moths can fly over vast distances and are most active at night. The male lives for 6 to 7 days, but the female lives for approximately 10 to 15 days, and lays about 92% of the eggs during the first two days after she emerges, and she can lay up to 260 eggs during her lifespan. The eggs hatch 4 to 5 days after being laid, and are small and cylindrical in shape, varying on colour from oyster-white to yellow. They are deposited mainly on the leaves, either as a single egg or in groups of 2 to 5
Click here to see Google images of the moths
There are usually four development stages (instars) of the larvae. During the first stage, they are white with a distinct dark head, but from the second instar onwards they turn a green and whitish-pink colour. Larvae are 0.9mm during the first instar, increasing in length to 7.5mm by the fourth instar. The younger larvae attack the leaves by tunnelling between the epidermis layers, later attacking the stems and fruit.
The tomato leaf miner can complete its life cycle in about three weeks in summer but it usually takes longer in cooler conditions. When they are mature they are usually fat and pinkish in colour and will search for a place to pupate and form a silk cocoon, either in the soil, or on the inside or outside surface of a healthy, unmined leaf. Pupation is usually 10 days but can be slower under cooler conditions. The insects can also overwinter as eggs or pupae, depending on the environmental conditions and availability of food.
Plant hosts for the tomato leaf miner includes species from the Solanacea family, but the main host is the tomato plant. Potatoes, eggplant and gooseberries are also potential hosts.
Tomato leaf miners usually reduce the quality and yield of the crop. The primary site of damage is the leaves, and as the larvae feed the tunnelling they create is unmistakable. Leaf miner can destroy younger plants, and although older plants are more tolerant, yield losses of 80 to 100% can occur. As the larvae develop they will move from the leaves to the fruit, usually via the flower calyx. Entry points are usually visible due to the ‘frass’ surrounding the area. These entry points are also sites for secondary infections, leading to fruit rot.
Click here to see Google images of the eggs, larvae and tunnelling of tomato leaf miners
Because tomato leaf miner is such a threat to commercial growers there are many products they use, but most are not available for gardeners. However, one product listed specifically for tomato leaf miner is Eco Insect Control by Efekto, and it is thankfully available to gardeners. It has as its active ingredient Spinosad, which is derived from the fermentation juices of a lowly soil bacterium called Saccharopolyspora spinosa.
To chemists, spinosad is a complex molecule known as a "glycosylated macrolactone" but for gardeners with a hankering for safer products, spinosad may be an organic godsend. Spinosad was granted organic status by the USDA National Organic Program in 2003 however few home gardeners are aware of its potential uses. It is moderately toxic to fish and toxic to aquatic organisms and honey bees so use correctly and do not spray when honey bees and other pollinators are very active.
Efekto ‘Eco Insect Control’ contains the active ingredient spinosad, and is used to control the following pests in lawns, outdoor ornamentals, vegetables, apples, citrus and stone fruits: American (African bollworm), thrips, potato leaf miner, American leaf miner, western flower thrip, and lawn caterpillar.
The Potato Leaf miner
The potato leaf miner (Liriomyza huidobrensis) was introduced into South Africa in 2000. Initially severe yield losses of up to 70% were experienced by potato farmers in the Sandveld region. After the registration of a few insecticides, the problem subsided during the following years. However, during some seasons the problem seems to become serious again. The potato leaf miner attacks many vegetables, including tomatoes, but on potatoes it is particularly severe.
The potato leaf miner adult is a small fly, so small they are not easy to observe. It is about 2mm with a bold yellow dot between its wings. The females puncture the leaves, making small holes, into which the eggs are laid, and when the minute larvae hatch they start mining the leaves. Affected foliage appears to be diseased and dies off prematurely. Yield loss is always due to the destruction of the foliage, as the maggots never mine into fruiting bodies or tubers.
African bollworm (Helicoverpa armigera)
African bollworm is the offspring of a night-flying moth, and a major pest of many crops. Because the larvae feed mainly on the flowers and fruit of tomatoes, bollworm and can cause huge losses if not controlled. As for tomato leaf miner discussed above, Efekto ‘Eco Insect Control’ is listed for control of this insect.
Pupation takes place in the soil, and the adult moth has a wingspan of 40mm, and a body length of 18mm. The forewings have two characteristic brown markings, while the hindwings have two distinct pale spots. The moth lays tiny creamy-white eggs singly on the flowers and leaves, and under good conditions they will hatch within three to five days. The young caterpillars are hairy, and vary from black to dark beige in colour.
After about two to three weeks the larvae are fully grown and up to 40mm long, with a characteristic broad white to pale yellow stripe on either side of the body, and small black spots on the upper side. Mature larval colours range from shades of green and reddish yellow, to reddish brown and black. In the warmer parts of KwaZulu-Natal, bollworm is present throughout the year, although populations are smaller during the cooler months (with temperatures below 18°C).
Click here to see Google images of African Bollworm.
I hope this article has been of value to you, and rather than depressing you with all the things that could kill your tomatoes, I hope it has inspired you to grow the best tomatoes on the block! Remember, some seasons are better than others, depending a lot on the weather, and mother-nature is sometimes pretty ruthless, and despite our best efforts there will be seasons when our crops fail, but that does not stop us growing again next season, because that’s what gardeners do. And when you bite into that first sun ripened tomato of the season, you know why it’s all worth it.
