Pests and Diseases
Diseases
The most common and problematic diseases of tomato plants in Central and South Texas are fungal foliage (rather than systemic) diseases such as Early Blight and Septoria Leaf Spot. We also occasionally see some minor Bacterial Spot/Speck, but have not found that these usually prevent the possibility of obtaining a good harvest here.
Early Blight
We may also encounter various fruit rots and spots later in the season, especially if rains are heavy. This can be due to a variety of reasons, including late blight, advanced/untreated early blight, pythium and alternaria rots, anthracnose, etc. Good cultural practices, including mulching, removing diseased fruits/foliage, and frequent picking can cut down on the frequency of fruit rots.
Blossom End Rot is not a disease at all but is instead a physiological issue with nutrient uptake. BER is typically caused by uneven watering/moisture and usually goes away later in the season. Its effects can be somewhat mitigated through proper watering techniques. We have found that the application of Dolomitic (not hydrated) lime can also be helpful, but you may not need it. If in doubt, have a soil test done first.
Blossom End Rot
Root Knot Nematodes can occasionally be a problem, especially for those with sandy soil. Nematodes cause root galling and affect the ability of the roots to uptake water and nutrients. Signs of a nematode infestation are visible bumps (galls) on the roots, wilting, yellowing of leaves, and stunted plants. Commonly suggested methods to control nematodes include planting cover crops of elbon rye, marigolds, or brassicas, but results vary. Amending the soil with lots of organic matter may also help, as well as rotating crops.
Some folks are getting good to great results by pretreating planting areas using mustard based products such as Dazitol, or even by just working some mustard powder into the planting hole when setting out their transplants. If you have problems with nematodes, yet another option is to grow in containers.
Actinovate might also be worth a try, and there is some anecdotal evidence out there to suggest that it might help to create a favorable environment for the roots to thrive and resist RKN. Adding sugar or molasses to the planting hole can also help.
Another option is to grow Nematode tolerant varieties (frequently hybrids) denoted by a “N” following the variety name in the catalog or on a plant tag description. However, we have found that most N tolerant varieties may not always be the most flavorful. Some we do like for taste include Sun Gold, Sweet Quartz, Mortgage Lifter VFN, and Momotaro — just to name a few.
Note: Tolerance does not mean complete resistance. If the infestation is severe, even N tolerant plants will eventually succumb, but it can buy you some time — perhaps enough time to get a good harvest.
Tomato Spotted Wilt Virus (TSWV) is a devastating tomato disease for some folks in the Panhandle, but is not generally seen that much in Central and South Texas at this time. TSWV is transmitted to tomato plants via thrips. Ways to minimize the possibility of TSWV include keeping weeds mowed and avoiding plantings of known host plants close to or in your gardening area. Specifically, be aware that marigolds are a common ornamental host plant for thrips (and spider mites) in our area, even though this goes somewhat against old garden lore that suggests marigolds are a good “companion” plant for tomatoes.
Tomato Spotted Wilt Virus courtesy MSUCares
Systemic fungal diseases might include Fusarium and Verticillium wilts. These are both in the soil and infect plants via the root system. Treatment options tend to be limited for both of these fungal wilts, but luckily, they are rather uncommon in our area. Bacterial wilts are also systemic, and also tend to be uncommon in our area.
General Disease Prevention Suggestions
- Watering — Water plants in the morning or early afternoon whenever possible, and water the soil, not the foliage. Do not be tempted to overwater. Water deeply and infrequently from the very beginning to train your plants, as this will tend to cause them to drive their roots deep (to seek water), which will lead to healthier plants that are better able to fight off various stresses. We generally prefer to water our plants no more than once every 4-5 days or so, even during the worst drought weather and hot temps. Soaker hoses are our preferred method of watering plants.
- Location — If at all possible, site your plants where they get good early morning sun so that foliage dries out quickly from any accumulation of overnight rain or morning dew.
- Mulch — Mulching can help in limiting splashback of fungal spores onto the foliage from the soil. It can also assist you in your efforts to water deeply and infrequently as a layer of mulch will significantly cut down on evaporation. Just be careful not to pile up too much mulch right up next to the stem — be sure to leave a gap of an inch or two to avoid stem rot. Several inches of pine or wheat straw, coastal hay, shredded black-and-white newspaper, shredded leaves, and untreated pine bark are possible mulch choices. Ideally, install your soaker hoses first, then put mulch on top of them to keep any wetting of the bottom foliage to a minimum.
- Spacing — Space plants 24″ to 36″ apart for proper airflow. This will tend to limit the chances of disease from spreading from plant-to-plant and will also avoid areas of dense foliage between plants where insects may hide.
- Removing diseased foliage — Remove and dispose of diseased foliage on your plants periodically to minimize the possibility of fungal disease spreading to the rest of your plants. Do not add diseased foliage to compost piles.
- Selective pruning — We generally don’t prune to a specific pattern such as a central leader or “suckering”. We have found that it is wise to leave most of the foliage on for both maximum photosynthesis and protection of the fruits from sunscald. However, we do perform light cleanup of foliage and occasionally some suckers below the first fruit or flower cluster (or the bottom 12″ of the plants, if first fruit set occurs higher up for whatever reason); as this can be helpful in allowing the plants to dry out more quickly after rains and morning dew. If plants become extremely cramped in their cages to the point that good airflow is inhibited, light thinning of the foliage is recommended.
- Daconil — Early in the season, we usually use a fungal preventative called Daconil (Chlorothalonil) to help the plants get off to a good start and reach a critical mass. Later in the season, we frequently don’t bother to continue spraying plants if they look healthy after significant fruit set has been achieved — especially in a dry year. Daconil is a non-systemic fungicide that coats the foliage in order to limit fungal spore attachment.
Daconil is not a cure-all, and will not reverse existing disease present on foliage. It is best used as a preventative from the get-go, applied early and regularly, if at all. Daconil can usually be found at most box stores or gardening centers labeled as either Ortho Garden Disease Control or Daconil in a 29.6% concentration. Mix up small batches following the instructions. Pre-mixed spray bottles of Daconil have poor application and are not cost effective if you are growing more than a couple of plants.
Sunscald
Pests
Stink bugs and Leaf-footed bugs are frequently a problem in our area because they will damage the fruit, leaving behind inedible corky white spots. Soap sprays and neem oil can help in controlling the immature bugs (nymphs), but may not have always much of an effect on mature bugs. Bugs and nymphs should be removed from plants and squashed whenever you see them. They can also be knocked into a bucket of very soapy water, or vacuumed off using a hand-held vacuum. Surround, a finely milled kaolin clay product which is mixed with water and sprayed onto the plants, will also tend to repel them. Trap crops such as millet can sometimes be effective if the stink bugs find those crops more attractive. Then, you can kill them on the millet. Chemical controls for stink bugs include Ortho Bug-b-Gon Max (Bifenthrin) and Sevin (Carbaryl).
Adult leaf-footed bugs
Leaf-footed nymphs
Note: Not every insect encountered in the garden is an enemy. Assassin Bugs can look similar in appearance to leaf-footed or stink bugs from a distance, but have distinct differences in leg formation and other distinguishing characteristics. Wheel bugs, a type of assassin bug, have a serrated “wheel” protruding from the top of the thorax. They are not harmful to your tomatoes, and are in fact a highly beneficial insect which will prey on many other insects in your garden. Assassin bugs usually travel alone which can be used to help identify them. Nymphs look similar to leaf-footed and stink bug nymphs, so keep that in mind and attempt to make a proper ID before reaching for a pesticide.
Keep an eye out for Cornworms and Fruitworms, as they will tend to bore into the fruits and cause damage. More often than not, fruitworms will eventually find your tomato plants, as will Tomato Hornworms. Hornworms can eat an amazing amount of foliage relative to their size, to the point that just a few insects can severely defoliate and damage your plants.
Note: If you find a hornworm that has been parasitized by Braconid wasps (white eggs on its back), leave it be, as these are beneficial wasps that will kill the hornworm before it does substantial damage.
B.T. (Bacillus Thuringiensis) is an organic dust (Dipel Dust) or liquid concentrate which will help to get these pests under control, that is best used early and regularly in the season to keep the population under control before they have a chance to multiply and do serious damage. Note: B.T. does not kill on contact. It is ingested by caterpillars when they feed on the foliage.
Fruitworm damage
Hormworm
Both Spider Mites and Whiteflies can sometimes be a problem, but usually tend to be less problematic in our area than the above-mentioned pests. Spider mites are much more frequently seen during dry/drought years, or in the more arid areas of Texas. Both can usually be controlled with regular use of soap sprays or neem oil, but it is important to become familiar with the early signs of damage — dulling of foliage and/or rasping (tiny lighter spots on leaves) — so you can treat if necessary before the population gets a foothold and does major damage to your plants.
A magnifying hand lens may be helpful in spotting them early on – look on the undersides of the leaves for moving dots and thin wispy webbing. We have found that severe spider mite infestations cannot always be effectively treated using soap sprays or neem oil, but we have had good success in the past using Pyganic (pyrethrin).
Note: Overuse of the broad spectrum insecticide Sevin has the potential to cause mite problems down the road, as it kills other insects that prey on them (Sevin is not effective against spider mites). You can end up with a double whammy effect by using it if your garden is prone to mite problems. Just keep that in mind before reaching for the Sevin dust and regularly coating your plants in it as a general all-purpose bug preventative.
Before using any garden product, please read the instructions and review any harvest withholding or picking guidelines on the label carefully. Most products are best applied in the morning, especially if application involves wetting the foliage. Even seemingly innocuous “homemade” tonics or soap sprays have the potential to burn your plants if used when temperatures are high or during direct midday sun. Please use recommended dilution rates as per label instructions — more is not better and can damage your plants or be toxic to you.
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