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)

Common Purslane: A Troublesome Summer Annual Weed

Common purslane is a weed of crevices between
bricks, in cracked cement, or compacted, low nutrient
soils. It also can be found in most cultivated crops,
gardens, lawns, and landscape beds (Photo: NMSU)

Featured Diagnosis: Common purslane (Portulaca oleracea) is a summer annual with a prostrate, mat-forming growth habit and thick, succulent stems and leaves. The plant germinates from seed during the warmer summer months (from March until August) and is a troublesome weed in cultivated fields, gardens, and landscapes throughout New Mexico. It is easily identified by its’ smooth reddish or flesh colored stems along with leaves that are succulent, shiny, green with maroon tinges, almost teardrop shaped, and wider at the tip than at the base. In late summer, the plant produces bright yellow flowers that have five petals and are only open when it is sunny. The plant also produces large amounts of viable black seeds that are produced in fleshy capsules that resemble unopened flower buds. These seeds have the ability to remain viable in the soil for multiple years before germinating.

Common purslane can be identified by it's smooth
reddish stems and shiny, succulent, teardrop-shaped
leaves (Photo: NMSU)

The bright yellow flowers of common purslane
are only open when sunny (Photo: NMSU)

Fleshy pods open at maturity to release multiple
tiny black seeds into the soil (Photo: NMSU)

Cucumber Mosaic Virus on Vegetable Plants

CMV on chile pepper (Photo: NMSU-PDC)

CMV on tomato (Photo: NMSU-PDC)

Featured Diagnosis - Cucumber Mosaic Virus. Are some of your vegetable plants deformed, twisted or elongated? Are the leaves mottled, wrinkled or curled? Are the plants stunted and not producing any fruit? If you answered yes to any of these questions, then your plants may be suffering from Cucumber Mosaic Virus (CMV). This is a common virus, worldwide, and is present every year in New Mexico. CMV can cause a wide range of symptoms depending on host, age of the plant, virus strain and environmental conditions. The disease is sometimes referred to as “shoestringing” because of the effect on young leaves to develop a narrow, elongated, tendril‐like appearance. Although common, this symptom is not always associated with infection. Other common symptoms include deformity, wrinkling, twisting, curling, yellowing (chlorosis), and mosaic or mottling.

Unfortunately, CMV doesn’t produce unique symptoms and diagnosis based solely on visual observations is risky. Many other viruses produce similar symptoms. Likewise, some herbicides may cause look-a-like damage. Whether or not there has been an herbicide application on or near affected plants is an important consideration in distinguishing between a virus disease and herbicide damage. The number of plants affected may also be a clue to the cause. Typically, a virus will affect a relatively small number of plants whereas herbicide injury may be more wide-spread. A laboratory test can confirm infection by CMV and/or other plant viruses.

Leaf symptoms of CMV on eggplant (left) and tomato (right)
(Photos: NMSU-PDC)

Entomosporium leaf spot on Indian Hawthorn

Entomosporium leaf spot on Indian hawthorn
(Photo: NMSU - PDC)

Featured Diagnosis: Entomosporium leaf spot on Indian hawthorn (Rhaphiolepis indica) – Entomosporium leaf spot is a fungal disease caused by Entomosporium sp. It is common on trees and shrubs in the rose (rosaceae) family. It can be particularly troublesome on Indian hawthorn and red tip photinia. In some areas, these shrubs are no longer widely used in the landscape because of their susceptibility to this disease. Other hosts of this pathogen include pyracantha, pear, quince, loquat, and mountain ash. The primary symptom of this disease is the development of reddish-purple spots on the foliage. The fungus produces characteristic “insect-shaped” spores which are diagnostic.

Characteristic "insect-shaped" spores
of Entomosporium sp. (Photo: NMSU-PDC)

Leaf spots on Indian hawthorn caused by
Entomosporium sp. (Photo: NMSU-PDC)

Pink Root on Onions

Pink root on onions caused by
Phoma terrestris
(Photo: NMSU-PDC)

Featured Diagnosis: Pink Root on Onions. Onion samples from Southern New Mexico recently submitted to the NMSU - Plant Diagnostic Clinic were infected with a disease known as pink root. Pink root is caused by the soil-borne fungus, Phoma terrestris. This pathogen is common in New Mexico and is problematic worldwide wherever onions are grown. The disease is especially devastating in warmer climates. Although many isolates of this fungus are specific to onion, some have the ability to infect other hosts including tomatoes, soybean, eggplant, pepper, spinach, carrots, small grains, cucurbits, corn and ryegrass.

Pycnidium and spores of Phoma terrestris
(Photo: NMSU-PDC)

The most noticeable symptom of the disease is the reddish-purple discoloration that occurs on infected roots. In the early stages of the disease, the color change in subtle, but the discoloration darkens as the disease progresses eventually leaving the roots stained dark purple. By the end of the season, infected roots have become dry and brittle and often disintegrate. Roots of infected plants become dysfunctional and plants will suffer from nutrient deficiency and drought. When young seedlings are infected, they may die; however, death is not the end result when more mature plants are infected. In this case, plants are stunted, exhibit leaf tip dieback and bulb size is reduced affecting overall yield and marketability.

Early symptoms (left) and late symptoms (right) of
pink root on onions (Photo: NMSU-PDC)

Summer Heat Brings on Symptoms of Bacterial Leaf Scorch in Chitalpa

A chitalpa tree infected with Xylella fastidiosa,
the causal agent of bacterial leaf scorch
(Photo: NMSU-PDC)

Featured Diagnosis - Bacterial Leaf Scorch of Chitalpa. Over the past week, several chitalpa samples have been submitted to the NMSU Plant Clinic exhibiting symptoms of leaf necrosis. Chitalpa trees (a hybrid between catalpa and desert willow) are susceptible to a xylem-limited bacterium called Xylella fastidiosa. The bacterium invades the plant and plugs up the water conducting vessels, known as the xylem vessels, making it difficult for the plant to get enough water to the leaves. The result on the plant is symptoms of water and nutrient stress - chlorosis and leaf scorch. Other symptoms include leaf spotting, small leaves, thin canopy, branch dieback, and eventually, tree death. This disease was first discovered in New Mexico in 2006. It was also confirmed in grapes the same year. In grapes, the disease is known as Pierce’s Disease. In 2010, the disease was also confirmed in catalpa and peach. The disease is transmitted from one plant to another through xylem-feeding insects, most notably sharpshooters. While New Mexico has some native sharpshooters, the most efficient vectors for Xylella, the glassy-winged sharpshooter and the smoke-tree sharpshooter, are not know to occur. 

Bacterial leaf scorch symptoms on chitalpa leaves
(Photo: NMSU-PDC)

Disease progression - the same tree photographed in
August 2006 and October 2006
(Photo: NMSU-PDC)

Tomato Spotted Wilt Virus Confirmed

Tomato infected with
TSWV (Photo: NMSU-PDC)

Tomato and chile pepper growers should be on the lookout for a potentially significant viral disease called Tomato Spotted Wilt Virus (TSWV). This virus was recently identified in the NMSU Plant Diagnostic Clinic on chile pepper samples from across the state. This virus is commonly identified in New Mexico. It has a wide host range that includes vegetable crops, ornamentals and weeds and it is transmitted by thrips which is a common insect pest. TSWV is an important disease of many different crops grown in temperate and subtropical regions of the world. It is a unique virus in a virus class by itself. The virus has a wide host range, but some of the more common hosts for New Mexico are tomatoes, peppers, potatoes, eggplant, peanuts, lettuce, cucurbits, many legumes, many ornamentals, and weeds such as field bindweed, nightshade, and curly dock. This disease is especially damaging in the ornamental and vegetable greenhouse industry.

TSWV on a pepper leaf
(Photo: NMSU-PDC)

TSWV on tomato leaf (Photo: NMSU-PDC)

TSWV symptoms on tomato and pepper fruit
(Photo: NMSU-PDC)