Page 35 - Griffin Gazette - July 2025
P. 35
Controlled Environment Agriculture (CEA) production becomes Here are some common heat-related disorders related to heat stress
increasingly challenging during the summer months. High heat, growers may face:
elevated relative humidity, and intense light levels contribute to stress Tip burn in lettuce is one of the most recognized calcium
in plants. This stress alters metabolic pathways, affecting growth and deficiency symptoms. It occurs under conditions of high humidity
development. At the molecular level, the cause can be simple, for and low air circulation and is worsened by poor root health. In head
example, an enzyme that becomes unstable and unfolds at elevated lettuce, tip burn often increases once the head closes, as inner leaves
temperatures. In production, this heat stress response can result in transpire less.
abiotic disorders that visibly impact fruit and produce quality. Pillow disease in cucumbers presents as scab-like spotting on
Heat-related stress can affect all stages of fruit development, from the rind and pithy flesh with large internal voids, also due to calcium
flowering and pollination to fruit set, maturity, and ripening. Daytime deficiency.
temperatures above 90°F, especially when paired with nighttime Blossom-end rot is another common disorder seen in tomatoes,
temperatures in the mid-70’s, can significantly reduce yields in peppers, and cucurbits, caused by localized calcium deficiency during
fruiting crops. Lettuce is particularly sensitive to heat stress. Where fruit development (Figure 1).
high temperatures are a concern, growers should consult their Griffin Calyx tip burn in strawberries results from low nighttime humidity.
Green Goods representative for heat-tolerant cultivars and take steps Unlike other crops, strawberries rely on root pressure, rather than
to reduce greenhouse temperatures as much as possible. transpiration, to move calcium into young, unexpanded tissues. High
humidity at night helps prevent water loss through the leaf cuticle,
Heat Mitigation allowing root pressure to build. While increasing daytime transpiration
Shading systems and cooling pads can lower greenhouse helps manage tip burn in crops like lettuce, in strawberries, the more
temperatures by 0 to 15°F, depending on environmental conditions. effective approach is to suppress non-stomatal transpiration at night.
Shade cloth and shade paint such as ReduSol and ReduHeat Calyx tip burn appears as browning along leaf edges, calyxes, and
are both effective methods of temperature reduction. Woven flower petals. Overhead fogging is recommended during the day to
aluminum and white shade cloth typically provide the most cooling, cool the growing space, while low-pressure misting below the bench
outperforming black or colored alternatives. Shade paints are usually at night helps reduce leaf and calyx burn. Weekly foliar sprays of
white. Some formulation also include additves to reflect infrared light calcium chloride dihydrate applied with a surfactant like CapSil (OMRI)
for better cooling. are recommended to enhance calcium tissue uptake during periods
Cooling pads or cooling walls are especially effective when ambient of stress.
relative humidity is low. At 70% RH, pads may lower greenhouse
temperatures by around 5°F. When RH drops to 50%, a cooling pad Figure 1. Blossom-end rot on tomato. Photo Credit:David Grist
system can reduce the temperature by 13 to 14°F when the outside
air is 90°F. Consult Griffin’s Construction Department to help identify
the proper solution for your specific operational needs. Unmanaged
heat stress can lead to several common physiological disorders in
CEA production.
Heat Stress & Calcium
Calcium uptake can be significantly reduced under high heat, even
though calcium deficiency is more commonly associated with cool,
humid conditions. Calcium moves passively through the plant via
water uptake. It only reaches new tissue at the growing tips when
water exits through open stomates during evapotranspiration.
When plants are overwhelmed by heat, they close their stomates
to conserve moisture and prevent drought stress, which also halts
transpiration and calcium transport. This mechanism is responsible
for a variety of disorders in greenhouse or field grown leafy and
fruiting vegetables such as lettuce, tomato, and strawberry.
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