Heavy Rains May Cause Plant Problems

Drought maps for the 2nd week in July -
2015 (top) and 2013 (bottom)
(http://droughtmonitor.unl.edu)

Heavy rains may cause plant problems for crop producers and homeowners – The recent heavy rains across much of New Mexico are helping to relieve drought conditions, however, a lot of water in a short period of time can cause problems for plants - especially when rain hits the same area with different storms over a short period of time. Plant diseases caused by microorganisms that require significant amounts of moisture and/or high humidity are usually limited by New Mexico’s typically dry climate. However, when environmental conditions favorable for disease development occur, it doesn’t take long for these pathogens to cause problems. Over the past few weeks, heavy rains have hit much of New Mexico and plants are beginning to show symptoms of disease. Native plants and xeric plants can be especially vulnerable to excessive moisture events. Diseases that are favored by these conditions include foliar diseases and root and crown rots, but plant pathogens aren’t always the cause of problems following excessive moisture. Roots may become dysfunctional from a lack of oxygen in the soil. Blackening or blighting of leaves, flowers and stems is a common symptom caused by many different organisms that cause foliar diseases. Plants growing close together or in locations with poor air circulation are especially susceptible to attack by microorganisms. Plants weakened by other environmental stress or other pests are also more susceptible. Plants which have been experiencing prolonged drought are especially vulnerable to root rot when the roots are exposed to excessive amounts of water. The long term damage caused by foliar diseases depends on the situation. Annual plants may die or become unsightly earlier than expected. Perennial plants that are going to shed leaves later in the fall may suffer little permanent damage to the plant, depending on how much of the plant is affected and how early in the growing season the damage occurs. Plants with root or vascular problems usually develop stem or branch dieback or die. Plants that were stressed due to other conditions before the heavy rains may succumb to the cumulative stresses.

Powdery mildew on yellow bird of paradise,
Caealpinia gilliesii
(Photo: NMSU-PDC)

Foliar blight on purple coneflower,
Echinacea purpurea (Photo: NMSU-PDC)

Premature fruit splitting can be caused by irregular water or too much water arriving
at a critical growing point during fruit development. This causes parts of the
fruit to ripen at different rates resulting in split, ruined fruit. (Photo: NMSU-PDC)