Featured Diagnosis: Honey locust Agrilus (Agrilus difficilis)

Upper and lower surfaces of adult Honey Locust Agrilus.
Actual size, ~ 3/8” long Photo:
J. Shaughney NMSU Arthropod Collection    

Agrilus difficilis, the ‘honey locust Agrilus’ and a close relative of ‘Emerald ash borer’ was identified in Central New Mexico infesting honey locust (Gleditsia triacanthos). The tree canopy was leafless and apparently lifeless down to some green sucker growth near the ground. Upon closer examination there were D-shaped emergence holes in the bark, peeling bark with multiple larval feeding trails on its inner surface and small, very thin, blackish beetles that died in their attempts to escape their host. All of these beetle-related observations are similar to those caused by ‘emerald ash borer,’ an exotic, invasive ash-tree killer not known to occur yet in New Mexico. Dr. Carol Sutherland presumptively identified the insect as  Agrilus difficilis, the ‘honey locust Agrilus’ and this was later confirmed by Dr. Zablotny of the United States Department of Agriculture. 

Emergence hole (D-shaped) made by an adult
 leaving the tree. R. Husted, Sandoval Co. MG.  

Inside of honey locust bark – severe vascular damage from
larval stage. The black objects are adult A. difficilis that died
 before it could chew its way through the bark.
Photo C. Sutherland NMSU-PDC    

This infested honey locust died
from the top down note the green
 sucker growth at the bottom.
Photo: R. Husted, Sandoval Co. MG.    

A. difficilis larvae extracted from honey locust. The two little
dark brown ‘splinters’ on the rear are characteristic
of certain Agrilus species. Photo C. Sutherland NMSU-PDC    

Phymatotrichum root rot appearing in Southern New Mexico

Pear tree infected with Phymatotrichopsis omnivora
(these two photos were taken one week apart)
(Photo: NMSU-PDC)

Characteristic cruciform (cross-shaped) hyphae of
Phymatotrichopsis omnivora (Photo: NMSU-PDC)

Featured Diagnosis: Phymatotrichum root rot. This disease is also commonly known as Texas root rot or cotton root rot. It is caused by the soil-borne fungus Phymatotrichopsis omnivora. The fungus has an extremely wide host range that affects more than 2,300 species of dicotyledonous (broad-leafed plants). This disease produces very distinctive symptoms on plants and characteristic fungal structures which make diagnosis relatively easy (assuming the plant specimens evaluate contain the appropriate material). The most noticeable symptom on plants is rapid death of the crown with leaves remaining attached to the plant. Although the plant may have been infected for some time, symptoms appear quickly making it seem as if the plants died in a matter of days! The fungus produces fungal strands on roots which produce characteristic cruciform (cross-shaped) hyphae. Observation of cruciform hyphae under the microscope is a confirmation of the disease. The fungus is VERY LIMITED geographically to parts of the Southwestern United States and Mexico. Even within its geographical boundaries, the fungus is spotty in occurrence. The pathogen may be so isolated that it is only found in small areas; areas small enough that only one or a few plants are affected. It may also be found in larger areas where many plants may be affected. It is found only at elevations below 5,000 feet. In New Mexico, the disease has been found only in the southern part of the state (see map).

If you are concerned that you may have a plant with this disease, please contact your local county extension agent for assistance in submitting specimens for diagnosis.

Read on for more information on pecan diseases

New Mexico Counties were Phymatotrichum
root rot has been confirmed since 1993

Spore mat on Phymatotrichopsis omnivora
on the soil (Photo: R. B. Hine,
University of Arizona)

Phymatotrichum root rot on cotton
(Photo: NMSU-PDC)

Fungal strands of Phymatotrichopsis omnivora
on a cotton root (left) and a pecan root (right)
(Photos: NMSU-PDC, left; and R. B. Hine,
University of Arizona, right)

Phymatotrichum root rot on pecan trees
(Photos: NMSU-PDC)

Phymatotrichum root rot on a pistachio
tree (Photo: NMSU-PDC)

Phymatotrichum root rot on Chinese pistache (left); Close up of leaves clinging to the branches (right);
Fungal strand from the roots of this tree (insert). (Photos: NMSU-PDC)

Featured Diagnosis: Leafhoppers.

Sycamore (Platanus sp.) tree exhibiting classic
"hopper-burn" symptom caused by leafhopper
 feeding. (Photo: NMSU-PDC)

Featured Diagnosis: Leafhoppers.  A number of sycamore (Platanus sp.) samples have been submitted to the plant diagnostic clinic with “hopper-burn” caused by leafhopper feeding. There are several species of Erythroneura that could be called ‘sycamore leafhoppers.’ These pests are whitish-yellow and about 1/8” long. Leafhoppers have piercing-sucking mouthparts and cause damage to leaves by piercing the foliage, sucking sap and leaving very tiny white dots on foliage where their mouthparts were inserted. The resulting damage appears as a white to yellowish-brown stippling of the leaves. Damage can be so extensive that injured leaves appear nearly white. Initially, feeding tends to be concentrated near the midrib, and then eventually covers most of the interveinal spaces of the leaf blade. Like other types of foliar damage, that caused by leafhoppers may reduce leaf photosynthesis which reduces the amount of carbohydrates produced and stored by the tree, ultimately decreasing vigor. Severe damage over multiple seasons could eventually reduce the tree's carbohydrate reserves, making effects of feeding damage more apparent. As with other indirect pest damage, factors such as tree vigor, tree age, drought stress, and damage by multiple pests could exacerbate the effect of leafhopper damage. Control of leafhoppers involves the application of a well-timed topical insecticide in the spring and as need throughout the growing season to keep the populations under control. 

Leaf stippling or "hopper-burn" caused by leafhopper feeding.
Early symptoms left and advanced symptoms right. (Photo: NMSU-PDC)

Leafhoppers (Erythroneura sp.) feeding on the underside of a sycamore leaf.
These insects are whitish-yellow and about 1/8” long. (Photo: NMSU-PDC)

Dissecting microscope image of Erythroneura leafhoppers.
Note the piercing mouthparts top right. (Photo: NMSU-PDC)

Southwestern Cotton Rust Diagnosed in Southern New Mexico

Southwestern cotton rust caused by Puccinia cacabata
(Photo: J. Idowu, NMSU)

Southwestern cotton rust, caused by Puccinia cacabata, has been found on cotton plants in Southern New Mexico. This disease occurs sporadically in the Southwestern U.S. but has the potential to cause serious economic losses up to 50% under favorable environmental conditions. The disease has a complex lifecycle requiring two different host plants, cotton (Gossypium spp.) and grama grass (Bouteloua spp.), to complete a full disease cycle. During summer rains, the spores produced on grama grass germinate to produce airborne spores which are carried up to eight miles and cause initial infections in cotton. There is no repeating spore stage on cotton. All new infections on cotton are dependent upon spore showers from grama grass. The spores produced on cotton can only infect grama grass. Disease incidence is usually erratic in New Mexico and depends on summer rains, high humidity and an infected source of grama grass for inoculum.

Rust lesions on the underside of a cotton
leaf (Photo: NMSU - PDC)

Rust lesions on the upper (left) and lower
(right) leaf surfaces (Photos: J. Idowu, NMSU,
left; and NMSU - PDC, right)

Young cotton rust lesions (left) and older cotton rust lesions (right)
(Photos: NMSU - PDC)

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)