Chapter 11 Temperature

Temperature Effects on Plants Growth and productivity can both be affected by unseasonable weather Unseasonably warm weather can cause some plants to flower too early Unseasonably cold weather can reduce crop yields

Cool-Season and Warm-Season Crops Cool-season crops barley, rye, fescue, cabbage, collards, lettuce, turnips, onions Warm-season crops cotton, corn, soybeans, grain sorghum, bermudagrass, beans, southern peas, tomatoes, peppers, cantaloupe, squash

Temperature and Dormancy Some plants drop their leaves and appear to be dead but are only resting, or dormant Even dormant plants can only survive down to a certain temperature and their ability to survive is affected by duration of cold weather, wind, their age and health, and soil moisture

Days Needed for Germination at Various Temperatures

U.S. Hardiness Zones Determine types of plants that will grow based on average annual minimum temperatures 11 zones, with Zone 1 being the coldest and Zone 11 the warmest Generally, colder zones are found at higher latitudes and higher elevations

Growing Degree Days (GDD) Used to estimate growth/development of plants/insects during growing season Development will only occur if temperature exceeds some minimum base temperature (Tbase) GDDs are calculated by subtracting Tbase from mean temperature for the day

Base Temperatures for GDDs for Crops and Insects

GDDs for Corn

Vernalization Promotion of flowering by cold treatment given to plants or embedded seeds May be reversed by exposure to warm temperatures before required time is up (devernalization) Plant site for perception of vernalization is areas of active cell division; meristem

Frost Classification and Damage

Temperature Stress Photosynthesis is slower at lower temperatures Absorption of minerals and water is determined by temperature Plants have minimum temperature below which they may be injured or killed High temperatures cause desiccation and may directly kill cell protoplasm

Thermoperiod Refers to daily temperature change Plants produce maximum growth when exposed to day temperature 10 to 15 degrees higher than night temperature Plant photosynthesizes (builds up) and respires (breaks down) during the day and slows down respiration at night