With hundreds of varieties in virtually every shape, size and color, tomatoes are a perennial favorite in the vegetable garden. While the plants are generally very easy to care for, tomato ailments frequently show up as a yellowing of the leaf. This is caused by any number of factors, including insect pests, disease or misuse of herbicides. Dead flowers on a tomato are usually caused by temperatures unsuitable for pollination; unpollinated flowers wither and turn brown, having outlived their purpose.
Brown and Dead Flowers
Tomato flowers require the right temperature range to successfully pollinate and set fruit. Overnight temperatures can be no lower than 50 degrees Fahrenheit, and ideally overnight temperatures should be above 70 degrees for the best fruit-set and tomato quality. Additionally, tomato flowers have difficulty successfully pollinating when daytime temperatures are above 95 degrees---high heat inhibits pollination. If a flower fails to pollinate within several days of opening, the flower turns brown and dies, eventually dropping from the plant.
Caused by the soilborne fungus Fusarium oxysporum, fusarium wilt is more of a problem with heirloom tomatoes and hybrid varieties which were not bred for disease resistance. Older leaves are the first to show symptoms by drooping downward and turning yellow, but because the disease blocks the vascular system of the plant, the plant's top often wilts during hot daylight hours but recovers at night. The best controls include removing the affected plant and practicing crop rotation so that peppers, tomatoes, eggplants and potatoes are not planted in the same spot from year to year; the fungus persists in soil and will be an ongoing problem.
Early blight is another fungal disease of tomatoes. The spores which cause early blight are spread primarily by wind, and can be exacerbated by warm, rainy spring weather. Blight shows up first as small, dark brown spots on the lower leaves of the plant, developing into large circular lesions with yellow margins. The disease progresses upward, so snip off affected leaves as soon as you suspect they may be infected. Do not compost blighted leaves, as the disease spreads by overwintering on tomato plant material. To manage especially bad infections, follow a seven-day spray schedule with a fungicide spray. Crop rotation also helps manage the incidence of blight.
Known as cucumber, tobacco and tomato mosaic virus, this pathogen survives even through commercial tobacco processing and can be transmitted to tomato plants simply by the touch of someone who smokes. The disease shows up as a yellow-green mottling of leaves, and no chemical control exists to inhibit the spread of the virus. Prevention is the only cure; always wash your hands before touching tomato plants, and do not overhandle them, especially if you are in contact with tobacco products of any kind.
Tomatoes are very sensitive to 2,4-D, a common weed killer used on lawns to eliminate broadleaf weeds like dandelions. Winds can carry spray up to a mile away, and even at those distances tomatoes exhibit symptoms including curled, twisted and yellowed leaves, dropped blossoms and cracked fruit. Affected leaves can closely resemble the damage caused by mosaic virus. Be sure that if you must apply 2,4-D on your lawn, you do so on a day when winds are calm. Tomatoes located downhill from a treated yard can also be affected.