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Question: All of my tomato fruit have white or light colored spots when they start to ripen. Often these spots are hard or even bitter tasting. What causes these spots to develop and what can I do to prevent them from ruining my crop?
Answer: The problems you are describing are a result of insect feeding. The most likely culprits are stink bugs or leaf footed bugs. These critters feed on developing fruit by inserting their mouthpart into the fruit to feed. The symptoms are believed to be due to a toxin injected into the fruit when feeding. This area of the fruit stops expanding, while the cells around the dead cells continue to expand by increasing their water content. The result is deformed fruit that appears to have dimples. When ripened or nearly ripened fruit is injured, the injection of toxic saliva merely kills a cluster of cells that later forms an off-color hard mass in the fruit, reducing fruit quality and producing a bad flavor to the fruit. The symptoms can appear on green or ripe fruit but are more noticeable on the ripe fruit. On the green fruit, the symptoms appear as whitish areas with indistinct borders. Spots may be from 1/16 to over 1⁄2 inch in diameter. On ripe fruit the spots are light colored usually yellow. Peeling back the skin shows the discolored areas as superficial, shiny, somewhat spongy masses of tissue composed of silvery white cells. The cloudy spots may be cut out if they are few and the rest of the fruit should be fine. Someone sent me a photo last week in which a yeast infection had started at the point of feeding.
The later in the season it gets the worse this condition becomes coinciding with the activity and feeding of the stink bugs and leaf footed bugs. These insects may be so few in number that they go unnoticed early but as the numbers build up the damage worsens. The insect problem is worse where weeds have not been adequately controlled or near row crops where they may migrate from these large fields to your garden.
One non-chemical method is to destroy eggs before they hatch or when they are very small. The eggs are barrel shaped and occur in neat clusters or rows on the plant leaves. You can see what they look like by doing a web image search of stink bug eggs or nymphs. I have heard that people who live in the country and have yard chickens and guinea fowl seldom have a problem with stink or leaf footed bugs. As a side benefit guinea fowl are a great "watch dog" but instead of getting fleas and ticks they eat them. I remember as a kid being afraid to walk by a neighbor's house because the fuss made by their guinea fowl.
Chemical control is difficult when populations get high this late in the season. The nymphs are not real difficult to kill but the adults can be a challenge. You may use chemicals containing bifenthrin, cyfluthrin, esfenvalerate and lambda-cyhalthrin according to the label directions. Make sure you follow the label prescribed waiting period from spray until harvest and wash the fruit in clean water before consuming.
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