Much-needed rain on Sunday has given agricultural producers some reprieve from the “flash-drought” that has been building across Ohio over the past few weeks. Ohio has seen abnormally-dry to moderate-drought conditions across much of the state, according to the U.S. Drought Monitor. The Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES) has activated its Rapid Response Team to address the dry weather and provide extension resources for agricultural communities, including commercial vegetable producers. More information can be found at the OSU Early Drought Response webpage.
Periods of drought have plagued humanity since agriculture began. In modern vegetable production systems, dry conditions can lead to issues at multiple levels. This article will unpack the impacts of drought on vegetable production and discuss possible solutions.
Crop moisture stress
Crops vary widely in their water use efficiency (WUE), i.e. the amount of carbon produced per unit of water taken up by the plant. Many grain crops have been specifically bred for high WUE to maintain productivity in dryland systems. Vegetable crops, on the other hand, have comparatively low WUE and are typically irrigated via drip tape or center-pivot. Due to their higher water needs in “normal” seasons, many vegetable growers are already set up for irrigation and so may not be witnessing as severe crop moisture stress as field crop growers who rely on the rain.
In addition to the lack of rain, temperatures in northwest Ohio climbed into the high 80s near the end of May. High temps can threaten young plants in other ways apart from increased water demand. When crops are transplanted into black plastic mulch they can be stressed by heat radiating off the mulch surface. Young plants can also be burnt if any plant tissue is contacting the black plastic, which may be common if soil moisture levels are below wilting point. Transplanting into wet soil, overhead irrigation, or applying kaolin clay to plastic mulch surfaces to temporarily increase sunlight reflection can help keep temperatures around the plant cool and conducive to crop health.
Dry weather pests
Hot, dry weather in the spring can lead to earlier and increased activity in plant pests like thrips, aphids, and spider mites. These insects thrive in warm and dry conditions, which is why infestations in greenhouse environments are common. Insect feeding can reduce crop yield and quality and the pests can also vector viruses that affect vegetable plants.
Outbreaks of thrips, aphids, and spider mites can be managed in part by supporting natural enemies of the pests. These include ladybeetles (adult and larvae), lacewing larvae, and minute pirate bugs. Aphids are also preyed upon by damsel bugs, assassin bugs, aphid predatory midges and several predatory wasps. Species of predatory thrips and mites can also help keep pest thrip and spider mite populations in check. Find information on identifying natural enemies in this guide from OSU Extension and this educational video from Dr. Mary Gardiner at OSU.
Insecticide/miticide recommendations can be found in the 2023 Midwest Vegetable Production Guide. Avoid broad-spectrum products to conserve natural enemy and pollinator populations in the field. Read more on the topic in this article from Zsofia Szendrei at Michigan State University.
Pests that prefer hot, dry conditions: aphids (top), thrips (middle), and spider mites (bottom). Photos by University of Illinois Extension (top), Ontario Ministry of Agriculture, Food and Rural Affairs (middle) and Mississippi State University Extension (bottom).
Drought conditions also have implications for early-season weed control. With low moisture in the topsoil, weed emergence may be delayed and prolonged. Applying layby residual herbicides is important to keep weeds under control until canopy closure. Weeds that are heat/drought stressed also do not respond to postemergent spray applications as well as vigorous weeds. Plant leaves develop a thicker, waxier cuticle to minimize water loss which can also reduce herbicide absorption. Adjuvant usage may be needed to improve conditions for herbicide uptake. Weed growth and metabolism is also slowed, which reduces movement of systemic herbicides around the plant. Spraying in the morning can be advantageous for weed control, not only because of calm winds, but also because targeting plants at a time of day when they are the least heat stressed can improve performance of systemic herbicides. Read more on this topic in this recent article from Erin Burns and Christy Sprague at Michigan State University.
Wildlife damage to crops can be worsened in hot, dry weather. Rodents and other vertebrates may increase feeding in vegetable fields when food and water is scarce elsewhere. Irrigation equipment may be damaged by wildlife (coyotes, mice, etc.) looking for a drink. Options for keeping away wildlife include netting, fencing, repellants, trapping, and other lethal/non-lethal deterrents. Resources include the Ohio DNR Nuisance Animal Control Manual and Wildlife Management Factsheets from the USDA/Michigan State University Extension.
Last but not least, the safety and well-being of agricultural workers is important to keep front of mind. Working in hot and dry conditions poses a risk of heat-related illnesses. Continuous hydration and proper attire can go a long way towards ensuring worker safety. Find more information on the major heat-related illnesses and their mitigation in this article from Penn State.
Dealing with drought-stressed crops and dusty fields can also take a toll on growers’ mental health. Ohio State University Extension offers resources to help handle farm stress. Farm worker/manager performance is dependent on good mental health, so be sure to take this aspect of your vegetable operation seriously.
To sum it up, hot and dry conditions impact multiple aspects of vegetable production. While the material here mainly addresses the consequences of a dry spring, drought can cause different issues depending on when in the growing season it occurs. OSU Extension is a resource to help vegetable growers through periods of drought by providing information and support. Please reach out to your county educator or a vegetable extension specialist to explore ways OSU Extension can help you make your vegetable operation more resilient to drought conditions.
Thank you to Ben Werling and Ben Phillips from Michigan State University Extension for observations and ideas that contributed to the writing of this article.
Vegetable Extension Educator
Ohio State University Extension