Heat, humidity impact tomato plant growth
by Patrick Sweatt TSU Extension Agent, Agriculture
Jul 13, 2014 | 1406 views | 0 0 comments | 4 4 recommendations | email to a friend | print


What’s red, round and inspires the most calls to the County Extension office in July?

If you guessed Frisbees or kickballs you’d be wrong, but if you guessed tomatoes, then I’d have to shake your hand.

The combination of heat, humidity and abundant downpours has provided an exceptional environment for a great number of diseases of tomatoes to flourish.

Since tomatoes grow all over Cleveland and Bradley County, it might help to be reminded of what to look for if your tomato plants start to look a bit different than they did even a week ago. The fact is, tomatoes are being grown all over Bradley County- in 100-foot rows, backyard garden patches, flower pots and even hydroponic towers.

Some are yellow, some are red, some are even pink or black, and some are fried while they’re still green (if you’re lucky). So how can we keep them growing and bountiful the rest of the season?

Well, one great way is to pay close attention to any changes in your plants’ leaves, stems and fruit. Here is a sampling of what we have been seeing:

- Bacterial Speck — This is a fungal infection that causes fruit to become badly marked with numerous tiny (1/32 to 1/16th inch) brown specks. This is actually one of several infections that causes tiny lesions, but is distinguishable because they have defined edges and lay close to the fruit.

- Early Blight — Look for the first signs of Early Blight on the older leaves of your tomato plants — they start out as dark brown spots and eventually develop a ringed “target” pattern. Eventually, the surrounding leaf tissues turn yellow and fall off, leaving tomato fruits prone to other problems. Blight can also affect the stems and fruit and will devastate a crop if not brought under control quickly.

- Septoria Leaf Spot — This is one that has been coming in quite a bit with the recent weather patterns. Septoria covers the leaf with (surprise) spots that may be numerous enough to cover the entire leaf, causing it to drop off. The spores of this fungal disease are spread by splashing rain and watering from above, so a good preventative strategy here is to water the base of tomato plants.

This is only a sampling of the tomato diseases we see on farms and in the office, but if you catch them early enough we can often give a recommendation for control. Bear in mind that every situation is different, but that through daily observation of your crop you can catch most problems before there is a significant problem.

Here are some ways that you can plan for success with your tomatoes at this point in the season (midsummer).

- Side-dress tomatoes with fertilizer or compost once fruits are at least 1 inch in diameter. Doing this too early will prevent fruit from forming, and by doing this at this point in the season, you will get the most out of your investment. Contact your local Extension Office with help with determining fertilizer rates.

- Water plants at the base, if possible. This will prevent the spread of fungal spores from leaf to leaf on infected plants and will keep infections from spreading further. Tomatoes need to be watered slowly and deeply, but you should still feel the soil beforehand to make sure that you are not overwatering (it should always be moist to touch).

- Use a mulch to cool down the soil and prevent evaporation. By spreading wood chips, straw or grass clippings in your vegetable rows you can reduce the number of fungal contaminants that reach the plant and conserve water. If you do use grass clippings from your lawn, be sure that your lawn is free of sprays (herbicides, pesticides) that will harm your vegetables.

- Lastly, take a break from the heat and think a little about next year. Consider your garden rotation and how you can rotate crops to break disease cycles.

Which varieties are yielding well? Which taste good/freeze well/make great salsa? And if you happen to think of it, take a second to call the County Extension Office and tell us how it’s all going — we’d love to hear about your gardens. (423) 728-7001