University of California Agriculture and Natural Resources released guidance on Apr. 18 addressing common nonliving (abiotic) disorders affecting tomato plants. The recommendations focus on issues such as blossom drop, abnormal fruit coloration, leaf rolling, blossom end rot, puffiness, and catfacing.
The guidance aims to help gardeners recognize problems that are often caused by environmental conditions or cultural practices rather than pests or diseases. Understanding these factors can improve crop yields and plant health.
According to the resource, blossom drop in tomatoes may result from low night temperatures below 55° F or high daytime temperatures above 90° F, excessive nitrogen fertilizer use, too much shade, early planting in spring, or using varieties not suited for the local climate. Hormone sprays may help set fruit during cool periods but are ineffective during hot weather. Other suggestions include tapping blossom stems at midday several times a week to aid pollination.
Yellowing of fruit instead of turning red is attributed to overexposure to sunlight. Maintaining strong plant growth for adequate leaf cover and providing partial shade during the hottest part of the day are recommended controls. Leaf rolling is linked with high light intensity and soil moisture when plants are heavily pruned; even watering and shading can reduce this problem.
Blossom end rot is described as a water-soaked spot at the fruit’s end that enlarges and darkens due to calcium imbalance aggravated by fluctuating soil moisture or high soil salt levels. Adding organic matter to retain water and avoiding heavy nitrogen fertilization can help prevent it; gypsum may be used if soils lack calcium.
Puffiness occurs when temperature extremes disrupt pollination or after heavy rainfall deters bees from visiting flowers. Catfacing involves cracks around the stem end due to rapid growth under fluctuating moisture levels; mulching helps moderate soil temperature changes.
Gardeners facing pest-related damage can consult resources such as UC Integrated Pest Management for Tomatoes (link) or contact local Master Gardener programs for support.
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