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Q. Why are some of my tomatoes getting dark rotten spots on the bottom of the fruit?
- P.B., Orlando, FL
A. "Your tomatoes have "blossom end rot" (BER), a physiological condition caused by a lack of calcium at the growing tip of the fruit. It is also a common problem on peppers. While your soil may have adequate calcium, fluctuations in soil moisture content from dry to wet really increase the incidence of BER. It is especially bad on the early fruit each summer and in sandy soils.
The damage occurs as cells die at the tip of the fruit. In time (and as the fruit grows) the spots enlarge and turn black. So, by the time you see it, the damage actually has already occurred some time back.
Remedies for BER include having a soil test to make sure calcium levels are adequate, adding organic matter to a sandy soil to increase its moisture holding capacity, and keeping plants evenly moist, especially during the development of the first fruits. A thick mulch will help maintain soil moisture."
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Q. I grew several tomatoes from seed. One is planted in a large container, the others are right in the garden. The plant in the container appears to be growing well, but after the flowers bloom they drop off without forming tomatoes. The plants growing right in the garden are doing better. What is wrong with the one in the container?
- F.F., NY
A. "When tomato blooms drop, it is usually due to either poor pollination or is a response to stress. Common stresses include improper or fluctuating soil moisture, extreme temperatures (both hot and cold), hot dry wind, nutrient imbalance, and disease. Since this plant is in a container, I suspect that improper soil moisture combined with hot weather is the culprit. Tomatoes are large plants and require large containers and sometimes daily or even twice-daily watering in order to stay evenly hydrated throughout the hottest days of summer. However, the soil must not remain saturated, so be sure the container has drainage holes. Also, since potting soil becomes depleted of nutrients over time, be sure to fertilizer the plant regularly.
Interestingly, the tomato's wild relatives, native to Peru and from which the domestic tomato was bred, were pollinated by a solitary bee. Since that bee doesn't live here and the plant isn't favored by local pollinators, tomatoes are usually described as "self-pollinating." However, the plants do better when pollinated by insects such as bumblebees. At the very least, the plants must be shaken, either by the wind or by hand, to cause the pollen to drop to the stigma. (Greenhouse tomato growers must provide some means to shake their plants.) By encouraging a variety of pollinators to visit your garden, primarily by keeping insecticide use to a minimum, you may be able to improve pollination. If your tomato is in a very sheltered spot out of the wind, giving it a gentle shake once in a while might help too."
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Q. "I have had a severe problem with tomato disease. The lower leaves turn yellow with black spots and the symptoms move up the plant. I remove the leaves when they start yellowing but if I am gone for a week, most of the plant is then consumed. Last year I put copper dust in the hole along with my compost. Could the disease also spread from my metal cages? I tried bleaching them one year but it did not make a difference. Is there anything you recommend?"
- WI
A. It sounds like your tomatoes are probably suffering from either early blight or septoria leaf spot, or both. These fungal diseases impossible to eradicate from the garden, but you can work around them well enough to get a good crop.
Start by planting disease-resistant varieties. Unfortunately, there are no known tomato varieties that are resistant to septoria, but it's a good start anyway. Rotate crops so that you don't plant tomatoes in the same spot more than once every 3 or 4 years, since the spores of septoria remain viable on dead plant material and seeds that linger in the soil. The spores of the early blight pathogen, Alternaria solani, are always floating around in the air and dust, so these measures won't help much there.
Copper is used as a fungicide, but it wouldn't be effective in the planting hole. It needs to be mixed according to label instruction sprayed upon the leaves to prevent infection. Continue to use cages, use a heavy layer of organic mulch on the soil to prevent spores in the soil from splashing on leaves, and water in the root zone of the plants, avoiding getting moisture on the leaves, since the fungi need moist leaf surfaces in order to grow.
Some people report good results using fungicidal soaps and neem oil sprays.
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Q. What should I do about the brown, twisting "roads" that are appearing on the leaves of all my tomato plants?
- R.P., Orlando, FL
A. "Those are leaf miner tunnels. A tiny fly-like insect lays an egg in the leaf. The egg hatches into a tiny larva that feeds between the upper and lower surfaces of the leaf making those squiggly lines you are seeing. Then the larva drops to the soil to pupate and return as an adult.
Insecticide sprays won't affect the larvae, since they are hidden inside the leaf. So the only "control" is to repeatedly spray the foliage to try to kill the adults. This requires lots of spraying and is just not necessary since the damage these insects do is usually not severe enough to warrant control. The secondary damage to beneficial insects caused by pesticides usually outweighs any benefits.
This 'minor miner' damage shouldn't affect your crop."
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Q. I planted 6 varieties of tomato seeds in a seed starter, and produced excellent plants, which I transplanted into the garden. I ended up with beautiful plants that had lush green foliage and a large number of green tomatoes. Just as the first of these were starting to color up, with an orange pinkish tinge on the fruit, the trouble started. The foliage began to turn yellow and develop brown spots, then the green fruits developed hard brown patches. The plants were supported on trellises off the ground and the soil around plants was covered with black plastic. Any idea what the problem was, and how I can prevent it from happening again?
- D.C., Derry, NH
A. "It's likely that one or more diseases attacked your tomatoes. It's difficult to diagnose exactly what disease is causing the leaf symptoms, and it's not all that critical to make a positive ID; the controls for most diseases are similar.
It sounds as though the tomatoes themselves suffered from sunscald. As the foliage died back the fruits were subjected to intense sunlight, which can cause discolored or hardened areas on the fruit. On healthy plants, the tomatoes are somewhat shaded by the foliage.
The first step is to choose at least some disease-resistant varieties. Then, be sure to provide a thick layer of mulch underneath plants, since many tomato diseases are soil-borne and spread when rain splashes soil up onto the leaves. Since your plants are trellised, this should help. Some people find they can slow down the spread of disease by diligently picking off affected leaves and removing them from the garden. There are some new organic, soap-based fungicides that are showing promise, and sprays made from neem oil also have shown some fungicidal properties."
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Q. Our tomatoes always get to about tennis ball size, then split open. Why does this happen? The only pest we've identified is whiteflies, which we've been hosing off.
- V.M., Yuma, AZ
A. "They most common cause of splitting fruit is water stress. Tomatoes are moisture sensitive and need a regular supply of water to thrive and produce fruit, especially in hot, dry conditions. Alternating wet and dry conditions can cause all sorts of problems on the fruit, including the splitting you describe. Be diligent in your watering, keeping the soil evenly moist. Water plants deeply, making sure that water is reaching down 12 inches deep, and add a layer of mulch on top of the soil to help maintain moisture.
Sometimes small cracks will heal over, sometimes not. Others times the cracks serve as an entry point for infection, so you may wish to harvest the cracked tomatoes. Some varieties are more resistant to cracking than others. If you continue to have problems, you might choose smaller size tomatoes, rather than the large beefsteak varieties, and look for those described as 'crack-resistant.' "
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Q. "Last August we went on a five-day vacation -- just in time for a five-day deluge. When we returned, we found our porch garden half-drowned. Despite our best efforts, the plants were never quite the same. The tomatoes were especially affected -- the foliage became stippled with brown spots that seemed to affect the undersides of leaves and spread rapidly.
I'm getting ready to start this year's garden, and I'd like to know how to avoid letting the spores that I'm sure are everywhere on my deck get the better of my young plants. I'm sterilizing all my pots and sweeping my pressure-treated wood deck, but the dense clouds of gray dust raised by my efforts are starting to make me think my deck is ground central for fungal diseases of all kinds, and anything I plant will be doomed. Any advice?"
-B.B., Cambridge, MA
A. "I can't say for sure which diseases affected your plants, but one of the most common problems for tomatoes is septoria leaf spot. It's almost impossible to avoid septoria on in the best of times, since the spores linger on infected plant debris and tomato seeds in the soil. But you can improve your chances by cleaning up plant debris, and by treating your plants regularly with a spray of compost tea. Compost tea is teeming with microbes that somehow (perhaps through competition for resources, or by stimulating plants' immune response) reduces the incidence of fungal disease. To make compost tea, mix one part mature compost that contains some manure with 5 parts water. Let the mixture sit for 2 weeks, then filter and spray at 2-week intervals. You can also mulch the soil in the containers to reduce the likelihood of spores splashing from soil to leaf surfaces during rain/watering. And be sure the containers have excellent drainage."
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Q. "Help! I found several large caterpillars munching on my tomatoes. What should I do to get rid of them?"
-L.K., Carlisle, PA
A. It sounds like you're seeing tomato hornworms, which can grow to an alarming size! Like most caterpillars, hornworms can be controlled by using Bt, Bacillis thuringiensis. However, since tomato hornworms can do a lot of damage in a short time, you may want to remove the ones you see by hand. Note: If you see a caterpillar with what looks like grains of rice all over it, relocate it elsewhere in the garden rather than killing it. It has been parasitized by a certain wasp laying its eggs on it. These small wasps are harmless to humans, but will help the hornworm population in check. (The parasitized hornworm will die anyway.)
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Q. I planted tomatoes this summer for the first time and had great success, no doubt due to the hot, sunny summer we had. However, we now have an infestation of tiny white flying insects that fly up by the hundreds when you touch the plant. There are also teeny black dots on the leaves, perhaps the eggs? What is this insect, is it a pest, and, if so, how do we control them?
-M. K., Denver, CO
A. It sounds as if you have whiteflies, which often show up late summer or early fall. They multiply rapidly when temperatures are warm, but will die off as cold approaches. They such the juices out of foliage, leaving behind tiny yellow spots, called stippling, which can weaken the plant. The best way to keep whiteflies at bay is to start early.
Next year, monitor your plants carefully and when you first notice the whiteflies, start the following control methods. You can still apply these methods this year, as well.
Start with the simplest method first, and if that isn't successful, move on from there. A strong blast of water from the hose often works. Spray underneath leaves where the whiteflies tend to cluster. Do this daily if you notice insects.
Whiteflies are attracted to the color yellow. You can purchase or make yellow "sticky" traps from yellow cardboard smeared with petroleum jelly. They fly to it and get stuck.
Soapy water sprays are another possibility. Use 1 teaspoon to 2 tablespoons of liquid soap per gallon of water. Use regular, not concentrated soap. Don't use soaps with lemon, as the citric acid can burn plants. Start with the lower amount and work up as needed. Spray as often as needed. As with any spray you might wish to test it on a few leaves first before you treat all your plants. Spray early in the
morning before the sun heats up.
Next on my list would be an insecticidal soap spray. The insecticidal soaps are made from plant-derived fatty acids and target soft-bodied insects. Unfortunately, there's really no way you can target the bad guys without at least some effect on the good guys. If you can regularly monitor and tolerate some damage to your plants, over time Mother Nature strikes a balance, with the beneficials coming in to
control the bad guys. Healthy, vigorous plants will withstand insect attacks better than weakly growing ones, so providing the optimal growing environment is the first step in preventing prevent insect problems.
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