Heat Stops Tomatoes from Setting Fruit

Temperatures that remain above 75 degrees F at night and day temperatures above 95 degrees F with dry, hot winds will cause poor fruit set on tomatoes. High temperatures interfere with pollen viability and/or cause excessive style growth leading to a lack of pollination.

It usually takes about 3 weeks for tomato flowers to develop into fruit large enough to notice that something is wrong and an additional week before tomatoes are full size and ready to start ripening.

Though there are “heat-set” tomatoes such as Florida 91, Sun Leaper and Sun Master that will set fruit at higher temperatures, that difference is normally only 2 to 3 degrees. Cooler temperatures will allow flowers to resume fruit set.

Articles reprinted from the K-State Research & Extension Horticulture Newsletter

Orange Tomatoes and Heat

Tomato color can be affected by heat. When temperatures rise above 95 degrees F, red pigments don’t form properly though the orange and yellow pigments do. This results in orange fruit. This doesn’t affect the edibility of the tomato, but often gardeners want that deep red color back. Though you can’t change the color of tomatoes that have completely ripened, you can pick them when they are just starting to turn and have them ripen in cooler temperatures (75 to 85 degrees F is best). Such tomatoes will develop normal coloration.

Articles reprinted from the K-State Research & Extension Horticulture Newsletter

Squash Vine Borer

If you have squash or related plants that suddenly wilt and die, you may have squash vine borer. This insect will bore into the stems of squash, zucchini, pumpkins and gourds. Hubbard squash are a favorite, and butternuts are less likely to be attacked than other squash. Cucumbers and melons are usually not a target, although both can be affected by a disease that causes similar symptoms, known as bacterial wilt. (See the May 13 issue of this newsletter.)

The adult of this insect is a clear-winged moth that resembles a wasp. The forewings are a dark metallic green but the rear wings are clear. The abdomen is orange with black spots. The larva is cream-colored and rather wrinkled. Adults emerge in the spring and lay eggs on or near susceptible plants. Larva bore into the plant and feed for about a month as they move toward the base. Mature larva will exit the plant, burrow into the soil and pupate where they remain until the next year. Each plant can have numerous borers.

If you suspect squash vine borer, split the stem of a collapsed plant near where it enters the ground. Infested plants will be hollowed out and mushy and may contain borers. Unfortunately, there isn’t much you can do at this late stage. Control measures should center on prevention. Suggested preventative controls would include crushing the dull red eggs before they hatch, excavating larvae from stems before they cause much damage or using insecticide applications. Applications should begin when the vines begin to run and reapplied every seven to 10 days for three to five weeks. Direct the spray at the crown of the plant and the base of runners. Effective insecticides would include permethrin (numerous trade names), esfenvalerate (Monterey Bug Buster).

Articles reprinted from the K-State Research & Extension Horticulture Newsletter

Common Smut on Sweet Corn

Smut (Ustilago maydis) is a fungal disease of corn that may infect leaves, stems or ears though infections on ears are the most obvious. Immature galls are white and spongy but become brown with dark powdery spores with maturity. Leaf galls remain small but those on the ears or stems can become rather large and will release large numbers of spores when they rupture. This disease is likely to be most severe on plants injured by hail, cultivation or insects and tends to be worse on soils that have had heavy applications of nitrogen fertilizer or manure. Also anything that slows growth such as hot, dry weather or cool, wet weather when the plants are young can result in more infections.

Immature smut galls are considered an edible delicacy known as cuitlacoche in Mexico. They are a high value crop for some growers in the northeast U.S. who sell them to Mexican restaurants.

There is no chemical control for this disease. Crop rotation and a balanced fertilizer program can help minimize this disease. Remove and destroy galls from infected plants before they rupture.

Articles reprinted from the K-State Research & Extension Horticulture Newsletter

Hornworms on Tomato

Tobacco and tomato hornworms are the big green worms with spiny tails that cause rapid defoliation of tomato plants. By the time hornworms are detected, they are nearly full-grown and getting ready to pupate. The damage is done and there is little point in applying insecticidal sprays to kill them.

This early in the season you might wonder if you can prevent the appearance of these worms. From my tomato growing experiences, the answer is no.

Moths deposit eggs on tomato foliage. Although fairly large and readily visible without magnification, eggs are seldom seen because their green egg color helps them blend in to the leafy background. Newly hatched 1.5 mm long larvae are equally difficult to observe. Only after grown larvae have consumed foliage do they attract attention.

Despite knowing a big worm is present, finding it requires patience. If you do find one, there are two options – pick and discard, or let live. Although picking and discarding may seem satisfying — one less moth means fewer future worms — eliminating one worm will not make a big difference. It may be better to adopt the idiom “live and let live” and accept coexistence with these overall harmless creatures.

Articles reprinted from the K-State Research & Extension Horticulture Newsletter

Herbicides for Home Vegetable Gardens

Though mulches and hoeing are usually all that is needed for small vegetable gardens, homeowners with large areas may need the help of herbicides to keep ahead of the weeds. There is one preemergence and one postemergence herbicide that can be used on home vegetable gardens.

The preemergence herbicide is trifluralin. Preemergence herbicides kill weed seeds as they germinate. They usually have no effect on weeds that have emerged. Therefore, they must be put on either before weeds come up in the spring or after weeds have been physically removed. The preemergence herbicide trifluralin is sold under the trade names of Treflan, Preen, Miracle-Gro Garden Weed Preventer, Gordon’s Garden Weed Preventer Granules and Monterey Vegetable and Ornamental Weeder.

The postemergence herbicide is sethoxydim. This product will only kill grasses; broadleaves are not affected. However, it can be sprayed directly over the top of many vegetables. Sethoxydim is sold as Poast, Monterey Grass Getter and Hi-Yield Grass Killer. A second postemergence herbicide called fluazifop-p-butyl is labeled for commercial growers as Fusilade, but I haven’t found vegetables listed on the homeowner labels, “Over the Top Grass Killer” and “Grass-No-More.”

Also, the other homeowner products mentioned above often do not have as many vegetables on the label as the commercial products. Even among the homeowner products with the same active ingredient, there may be slight differences among labels. Check product labels to be sure the crop is listed. Here is a list of the various herbicides and the crops for which they are labeled. Note that many of these crops will have application restrictions. For example, trifluralin can be used on asparagus, but must be applied before spears emerge.

Vegetable	Treflan	Poast
Asparagus	X	X
Beans	X	X
Broccoli	X	X
Cabbage	X	X
Carrot	X
Cauliflower	X	X
Corn, Sweet
Cucumber	X	X
Eggplant		X
Lettuce		X
Greens	X
Muskmelon	X	X
Okra	X
Onion		X
Peas	X	X
Pepper	X	X
Potato	X	X
Pumpkin		X
Spinach		X
Squash		X
Sweetpotato
Tomato	X	X
Turnip	X
Watermelon	X	X

Cure the Itch by Planting Peas

If you are tired of winter and hunger for spring, try planting peas as soon as the soil dries and the soil temperature reaches 40 degrees. We have several types of peas we can plant in Missouri and Kansas. Probably the most common is the shelling pea and the old standard in this group is Little Marvel. Though Little Marvel is still on our recommended list, we have a number of others that do well including Green Arrow, Knight, Maestro, Burpeeana and Mr. Big. All of these are early maturing types that allow us to harvest a crop before the hot weather arrives and stops production. Snow peas are those commonly used in stir-fry that have a crisp edible pod. Recommended varieties include Dwarf Grey Sugar, Mammoth Melting Sugar and Snow Green. Sugar snap peas resemble shelling peas but have a thick, fleshy pod and can be eaten fresh, steamed or cooked. Like snow peas, they are not shelled but eaten pod and all. We recommend Sugar Bon, Sugar Ann, Super Sugar Snap and Sugar Sprint.

Peas should be planted shallow, about one-half inch deep, to encourage rapid germination and emergence. Seed in the row should be spaced 2 inches apart. Many people often plant two rows 6 to 8 inches apart so the floppy plants can support one another. For some older varieties, this may not be enough. They may need trellising to support the growing vines. Fencing may be needed to keep rabbits away.

All-America Selection Winners for 2010

All-America Selections tests and introduces new flowers and vegetables each year that have done well in trials across North America. This year there was eight flower winners and one vegetable winner.

For more detailed information including how to grow, see http://www.all-americaselections.org/Winners.asp