Heat Stress Noted Among Many Texas Dryland Crops

Heat is stressing crops, pastures and gardens throughout Texas.

The majority of Texas A&M AgriLife Extension Service districts reported daytime temperatures exceeding the high 90s, with several reporting temperatures beyond 105 degrees. Increased daytime and nighttime heat is taking a toll on croplands and forages as moisture levels in non-irrigated fields continue to decline.

Lee Tarpley, Texas A&M AgriLife Research plant physiologist, Beaumont, said higher than normal temperatures around the state could impact yields and quality for producers.

Tarpley said there were reports from rice fields west of Houston regarding stress from high nighttime temperatures. High nighttime temperatures can affect rice flowering, which could hurt fertility and ultimately grain production.

A healthy range of nighttime temperatures for rice is below 73 degrees, Tarpley said. Anything above 77 degrees can noticeably damage plants.

Temperatures and heat stress can affect plants in several ways at different growth stages, he said.

During vegetative growth, heat stress can cause oxidative stress, which hurts plant photosynthesis, Tarpley said. Damages can impact yields.

Heat stress during flowering and seed setting, as with the rice fields near Houston, can impact fertilization and effectively reduce seed set and fruit or grain numbers, depending on the crop, he said. After the plant’s grain or fruit has started to develop, heat stress can hurt harvest quality.

Tarpley said high temperatures also impact plant transpiration, the process of water moving through a plant with most eventually being lost from aerial parts, especially leaves stems and flowers, as the plant exchanges gas with the atmosphere during photosynthesis. Transpiration has a cooling effect on plants, so can help reduce heat stress effects.

“At a point though, if the plant gets too stressed it will tend to shut down transpiration to leaves and flowers,” he said. “Dryland crops could be suffering without water. They try to take up more water, which indirectly takes even more energy.”

Tarpley said various crops are facing stress at different points in their growth cycle based on regional planting schedules and whether producers were delayed due to spring rains.

Delays that shift plant development deeper into summer usually have a detrimental effect on yields, said Dr. Ted Wilson, Texas A&M AgriLife Research and Extension Center director, Beaumont, because later maturing rice experiences higher temperatures, which increase plant stress.

A multi-year analysis of yields from over 10,000 rice fields showed yields decreased by 315 pounds per acre each week harvest was delayed past the week maximum yield occurs.

“If they’re delayed six weeks, you’re looking at almost 2,000 pounds per acre and that is significant,” he said.

The heat has different effects on various vegetative plants, but high temperatures cause stress for most crops at some point, Wilson said. Heat stress has been shown to reduce fruit sets in tomatoes, and a study on cotton by the University of California at Berkeley showed stressed plants began aborting young squares in which the plant has invested the least amount of energy so it might save bolls with heavy energy investment.

AgriLife Extension district summaries can be found here.

Source: Texas AgriLife Extension

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