The Perfect Storm for Tomatoes

— Written By Roger Galloway and last updated by Dawn Stone

The term “perfect storm” was first used as a weather term after a series of seven factors led to a March 20, 1936 flood in Port Arthur, Texas. However most of us remember the book or movie describing the 1991 Halloween Nor’easter storm.

Some Randolph County gardeners and farmers will remember the summer of 2012 as a perfect storm for tomatoes as a series of meteorological events contributed to the ruin of many delicious tomato sandwiches.

For many tomato cultivars the optimal night temperature for flowers to set fruit is in the 59 F to 68 F range and temperatures slightly above and below this range begin to reduce fruit set. Day temperatures above 85F to 90F also limit fruit set and in addition the humidity and duration of the temperatures play a role. I counted 8 days in June with days above 85 F and 3 nights below 55 F. In July there were 19 days above 85 F, 15 days above 90 F and 8 nights above 72 F. The tomato plants in my garden like many in the county have no fruits on the lower part of the plants because of the extreme temperatures.

Lack of rain and the timing of thundershowers also contributed to the perfect storm. First, dry soil conditions contributed to blossom end rot on the fruit by limiting the calcium uptake necessary for healthy fruit development. Then the late afternoon and night showers wet the foliage during the hours of darkness providing sufficient hours of wetness for early blight spores to germinate and enter the leaf tissues. Now most of the tomato plants in home gardens have brown and yellow leaves up to half the height of the plants, which makes fungicidal sprays with daconil (Chlorothalonil) questionable at this point in the disease progression.

Next year to improve the chances of weathering another perfect storm: plant some hot set cultivars which have the ability to set fruit in hot temperatures, consider using mulch and irrigation with a soil analysis to insure adequate calcium. Also a foliar spray of 3 tablespoon of calcium nitrate in a gallon of water may be applied 2 or 3 times after fruit set, at one week intervals. To manage early blight:  don’t wet the leaves just before dark and consider starting chlorothalonil or another fungicidal spray material after the fruit set stage and continuing to a period before harvest.

“There isn’t much you can do about the weather”, but there are a number of practices to better manage it effects.

Roger Galloway is a retired extension agent working in a part-time temporary position with the Randolph County Center of the North Carolina Cooperative Extension Service. He can be reached at (336) 318-6000.

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conform to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.