Southwest Michigan vegetable update – Aug. 16, 2017
Mites are increasing on susceptible crops.
Temperatures were again slightly below normal with highs from 73 degrees Fahrenheit to 84 F and lows from 51 F to 64 F. We continue to fall behind in growing degree-days (GDD). We are approximately 334 GDD behind 2016 and 76 GDD behind the five-year base 50 average.
We received approximately 0.2 inch of rain for the week and have had just a little over an inch for the past month. Most unirrigated crops are show signs of stress.
Virus symptoms are now present in vine crops. Nothing can be done once plants show symptoms. Aphids spread virus and generally, controlling the aphid has little effect in controlling virus spread. Aphid control products require the aphid to feed and once an infected aphid has pierced the plant, it has successfully transmitted the virus. A number of viruses are possible and the only way to distinguish them is to have a diagnostic test.
Mite populations are increasing on susceptible crops, notably tomatoes and watermelon. This is not surprising given the dry weather over the past month. Wet weather helps keep the population down by knocking mites off the plants and once off the plant they have difficulty finding their way back.
Excessive aphids are present on some sweet corn. Aphids generally only become a problem when they get on flag leaves of the ears. When they get on flag leaves, sooty mold generally follows, which is not problem for the plant but is a problem when it comes to sales.
For the past several years, I have been struggling with green core in tomatoes. Green core is a condition where the outside of the tomato fruit looks perfect, but when it is cut open there is hard, yellow/green/white tissue in the core (see photo). Not only is it visually unappealing, but it also is not a very pleasant experience to eat.
While at a meeting this past winter, a colleague from another state suggested it was due to excessive potassium. In the past, I would apply potassium according to the soil test as a broadcast prior to planting and then add more through the drip system. This year, I only did a broadcast application of 0-0-61 (150 pounds per acre) and none through the drip, and I do not have the problem.
If your tomato fruit is showing this condition, Michigan State University Extension recommends lowering the potassium rate to see if that will reduce symptoms.