Back to Glossary A - Z

Damping-off A disease caused by a number of fungi, mainly Pythium, Rhizoctonia, and Phytophthora. The symptoms include decay of seeds prior to germination; r rof seedlings before emergence from the root medium; and development of stem rot at the soil line after emergence, causing seedlings to topple. (Nelson, 2003) Detailed review of damping-off.

Day-neutral plant A plant that does not respond to the relative lengths of light and darkness in the daily cycle. (Nelson, 2003)

Depreciation Decline in value of an asset due to such factors as wear of obsolescence. (Nelson, 2003)

Desiccation The process of drying. Desiccation of plants results from a lack of water. High levels of soluble salts in the root medium cause desiccation of roots by preventing water from entering the roots. (Nelson, 2003)

Detergent See Surfactant. (Nelson, 2003)

DIF The difference between day and night temperature computed by subtracting the night temperature from the day temperature. By controlling DIF, the length of stem internodes (overall plant height) can be controlled. For many crops, the lower the DIF value is, the shorter the plant will be. (Nelson, 2003)

Disbudding The process of removing flower buds from a plant stem, generally to improve the size of the remaining bud or buds. In most cases, the terminal flower bud is retained and all of the lateral (side) flower buds are removed. (Nelson, 2003)

Disease A plant is said to be diseased when it develops a different appearance or changes physiologically from the normally accepted state. These differences are called symptoms. Disease can be caused by unfavorable environmental conditions such as temperature extremes, insects, or pathogenic organisms such as nematodes, fungi, bacteria, or viruses. (Nelson, 2003)

Distribution tube A clear plastic tube with holes alone either side that is installed along the length of a greenhouse to provide uniform distribution of air within the greenhouse. (Nelson, 2003)

Dry matter The portion of the plant remaining after water has been driven off. For purposes of foliar analysis, leaves are generally dried for one day at a temperature of 158ºF (70ºC). (Nelson, 2003)