Howdy Grow Appalachians! Boy, sure things have been moving at the speed of light here at HQ. Between holiday weekends, partner site visits, high tunnel videos, and mid-year reports and all their glory, it’s hard to believe that yet another month has come and gone just like that! But real life doesn’t stop, especially for gardens, and this week I’ll hopefully be helping share some resources/knowledge on combating pests and diseases among what is probably the most beloved crop in the garden: the tomato.
Ahh, tomatoes! Nothing really says “summertime” like plucking a garden-fresh tomato straight off the vine, taking it inside and scrubbing it off while it’s still warm, and then slicing it up….heaven on earth, if you ask me! But like any other yumminess growing in the garden, as much as we all probably wish it was true, you can’t plant your plants and then just walk away hoping for fresh goods a few weeks or months later. We’ll be looking at a few pests and diseases among tomatoes and how you can control them.
Diseases:
- Tomato blight: “Blight” is a term that is often thrown around in the garden world, but it can be fungal or bacterial. For the sake of tomatoes, we’re looking at the fungal version of blight. Blight is catastrophic to the plant once it becomes infected, and its viability is greatly reduced not long after, so it’s important to carefully monitor plants for any signs of disease early on. Development of blight is accelerated by warm temperatures in prolonged wet conditions, so think a summer storm. Potential blight damage includes yellowing or browning leaves, soft browning spots on the fruit (like a bruise), or lesions on the stem or foliage. Remove any potentially infected plant material immediately and destroy it. If fungicide must be applied, per application instructions, apply the product to the base of the plant, as less frequent but consistent applications is more effective than over-spraying. Please read all product labels! And remember, if you are affiliated with Grow Appalachia in any way, your product MUST be organic!
There are also two types of blight, early and late blight, which refer to the relative time in the growing season at which they can appear:
Early blight: Favored by warm temperatures and high humidity, early blight is caused by a fungus and it does not affect younger plants. Signs of damage usually first appear on older leaves as tiny brown papery flecks, which can grow into brown-black circular areas, bordered by a yellowish-green ring. Once the leaves die they typically don’t fall off. Darker spots can also be found on stems.
Late blight: Also caused by a fungus (though a different strain than the early blight), late blight is a devastating disease that, with favorable conditions, can kill an entire plant in two weeks. This type of blight, opposite of early blight, favors cool and moist conditions. Damage begins as small, irregularly shaped pale to dark green spots, and the spots grow to large brown or purplish-black. As the cool and moist conditions persist, a white fungal growth appears on the edges of the decaying areas, usually on the undersides of the leaves. Spots usually are found first on lower leaves. - Blossom end rot: Blossom end rot is a tricky disease, in the sense that many fungicidal efforts are not effective, therefore any control measures for this disease are primarily focused on the environment of the plant. BER is caused by inadequate soil aeration/drainage and insufficient calcium levels. Prolonged dry conditions accelerate the disease; the roots weaken and are no longer able to uptake and absorb nutrients and water. Damage appears at the blossom end of the plant, hence the disease’s name, and water-soaked spots may start small, but can soon enlarge to take up 1/3-1/2 of the fruit. Additionally, plants that are planted too early in soil that is too cool are also susceptible. For control, purchase a soil thermometer to assure that your soil’s temperature is at the optimum range for planting. Be sure not to over water, and, if needed, apply a fertilizer with higher levels of phosphorus (Also why it’s important to have your soil tested).
- Bacterial leaf spot: Also falling under an umbrella of diseases like blight, bacterial leaf spot is a common enough ailment that it has its own category. Look for slightly raised brown spots that look like scabs on the leaves. Neighboring plants that are also infected may spread the disease, especially during humid and wet weather. Remove any damaged leaves as they appear; this may slow infection. When you water your tomatoes, avoid watering the leaves; keep them as dry as possible.
- Fusarium wilt: A soil fungus that thrives in warm climates where summers have days above 80 degrees F (yikes!), the Fusarium bacteria enter the plant through the roots and reproduce in the plant’s vascular system. First signs of damage appear on individual stems, and plants typically grow normally until fruit begins to set, after which yellow wilting occurs. As the disease progresses, more stems and leaves yellow and wilt until the plant collapses. Yellowing is often present in the midsection of the plant, as are brown streaks if the stem is cut across. Fortunately, many tomato varieties are resistant, so select resistant varieties when planting. Also, practicing crop rotation ensures that plants are not planted in the same potentially diseased soil twice.
Trellising helps to keep growing plants (and fruit) off the ground
A few overarching control methods for disease:
-Practice crop rotation!
-Mulch, mulch, mulch! Not only does mulch help regulate plant moisture and weed pressure, it also prevents water and soil splashing onto the plant. Many damaging microbes reside in the top three inches of soil.
-Select and plant resistant varieties. When making your seed purchase, look for resistance codes on the package: EB or LB are for blight, F1-4 for fusarium wilt, BLS for bacterial leaf spot. Unfortunately there are no resistant varieties for blossom end rot.
-Keep tomatoes trellised or staked so they’re off the ground.
-Read all labels when applying fungicides!
Pests:
As if we need any more reasons to remain hyper-vigilant against all that threaten our veggies, it’s not just diseases that we should look out for. There’s lots of little critters that roam, crawl and fly into our gardens. The key to pests is that complete elimination is not the main goal; rather, it is controlling the populations so that it doesn’t turn into a major infestation. Here’s a few to keep an eye out for, and how to make sure they don’t make a lunch or dinner out of your tomaters:
- Tomato hornworm: With their distinctive light green color, red posterior horn, and white diagonal stripes along their backs, these guys are nearly impossible to miss. Look for them on the undersides of leaves or along the stems. They feed on the entirety of the leaf, leaving only the mid-rib intact, higher up on the plant rather than towards the ground. With hornworms, handpicking is best: you can place them into a container of soapy water. Or do what our own David Cooke does, and snip them in half with garden shears. Seriously. Very unpleasant, I know…
- Stink bugs: Shield-shaped and either green or brown, stink bugs are partial to many ornamental plants, but they also feed on ripening tomato fruit. They inflict their damage with their piercing-sucking mouthparts, leaving behind yellowish lesions, although damage can vary depending on the life cycle of the insect. Adult bugs overwinter and become active in the springtime, where populations peak around July until early October.
- Thrips: Tiny, slender insects that vary in color from yellow to orange, thrips feed on flowers and blossoms in plants. This feeding results in fruit not developing or becoming deformed. Additionally, thrips sometimes feed on foliage and this may result in discoloration. Some species of thrips also are carriers of tomato spotted wilt virus, a disease that causes dark, halo-light lesions. If young plants are infected, they never go on to bear fruit.
- Flea beetles: All Solanaceous crops are susceptible to flea beetle attacks, but potatoes and eggplant don’t seem to be as susceptible. Flea beetles get their name from the creepy crawly they resemble (*shudder*) Like stink bugs, flea beetles overwinter and then re-emerge from hibernation sometime in March, feeding on both surfaces of leaves but primarily on the undersides. Look for small holes that look as if they’ve been chewed through.
For a more comprehensive list of tomato pests in this region, you can check out this list published by the University of Kentucky.
We love bees!
That pesky hornworm…
A few overarching practices for keeping pest populations at bay:
-Keep weeds under control. Heavily weeded areas are ideal breeding grounds and habitats for pests.
-It may sound gross (and it sort of is!), but get in the habit of checking your garden every day and hand-picking or squishing pests if you find them. Again, keep in mind that complete elimination is not feasible, but rather control is most ideal.
-Don’t over-crowd your plants when planting. Too close spacing can quickly accelerate pest damage.
-Realize that some insects in your garden is not necessarily a bad thing. Some may actually be beneficial. A great resource is “Good Bug, Bad Bug”, an insect guide that helps identify both beneficial and problematic insects. We have two copies in our office!
-Be very careful with pesticides! As with fungicides and any other chemical control measures, please read every label, and apply only as directed. Some chemicals are very harmful to mammals and pollinators, especially bees. If you must use a pesticide, we recommend Spinosad, and you can purchase it off Amazon.
We all know gardening can be tough, and is certainly viewed as a labor of love, but a few practical steps and a few minutes a day of monitoring can mean the difference between a manageable issue and a rampant infestation. Keep up the good work, you all! As always, we are here for you for any questions and troubleshooting. Until next time, happy growing…and harvesting! I’m itching for some sungolds…
Resources/Further Reading:
Grow Appalachia HQ blog on pest identification
Clemson Extension tomato pests
University of Maryland extension: insect tomato pests
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