The latest Arizona Vegetable Integrated Pest Management (IPM) Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz.

Bagrada bug update: Summer populations

By John Palumbo, UA Research Scientist and Extension Specialist

I think we can finally conclude that Bagrada bugs have found a home in the desert southwest. Beginning in mid-April, pest control advisers (PCAs) reported Bagrada bugs on Brassica weeds, seed crops, and canola. By early May, the bug was found reproducing in these crops throughout the Yuma area.

Now, adults are found regularly in cotton. Numerous PCAs have reported picking up adults in sweep net samples; generally one to two adults per 50 sweeps with counts as high as 30 adults per 50 sweeps.

We previously speculated that cotton in the Yuma area may serve as a bridge to fall produce crops. However, we are uncertain whether Bagrada bugs can reproduce on cotton during the summer and cause feeding damage to squares and small bolls similar to other stinkbugs. Studies are underway in the laboratory and field to address these questions.

To date, we have determined that field-collected adults caged on cotton seedlings can live up to 40 days, but do not appear to be reproducing. There have been other reports out of California’s Imperial Valley of Bagrada bug adults on Bermuda grass and alfalfa seed crops. Adults have been swept from forage alfalfa in the Yuma Valley.

There is also a report from California’s Coachella Valley that Bagrada bugs are damaging peppers.

However, the most alarming observation thus far has been in the Imperial Valley. Last week I observed extremely high numbers of adults and nymphs feeding on a variety of plants including lemon trees, Russian thistle, and other unknown desert plants.

Presumably these populations developed during the spring on mustard weeds that were clearly abundant in the surrounding desert.

For a list of known host plants, and an updated list of crops and plants where Bagrada bugs have been found throughout the desert southwest.

Contact Palumbo: (928) 782-3836 or jpalumbo@ag.arizona.edu.

Plant disease resistance

By Mike Matheron, UA Extension Plant Pathologist

An extremely valuable piece of equipment in a plant disease management toolbox is the built-in resistance or tolerance to plant pathogens found in many types of plants.

By definition, resistance is the ability of a plant to exclude or overcome the effect of a plant pathogen, including a bacterium, fungus, virus, or nematode. Tolerance is the ability of a plant infected by a pathogen to grow without dying or sustaining serious injury or yield loss.

Resistance is not an all or nothing condition, but ranges from its highest level, immunity, through degrees of useful resistance to a level of nonexistence, when a plant is totally susceptible to a particular pathogen.

If available, it is wise to consider cultivars with known resistance or tolerance to one or more of the diseases of concern for that crop, as this disease management tool will be active in the plant for its lifetime.

Building disease resistance or tolerance into plants is an ongoing activity of plant breeders, using classical as well as modern genetic manipulation techniques to achieve this goal.

Contact Matheron: (928) 726-6856 or matheron@ag.arizona.edu.

Summer annual grass identification

By Barry Tickes, UA Area Agriculture Agent

Two closely related but different species of several summer annual grasses are common in the low deserts. These are easy to distinguish from each other in the field and all respond similarly to herbicides.

Some of these and the distinguishing characteristics include watergrass, Echinochloa colonum, and barnyardgrass,Echinochloa crusgalli. These are very similar. Watergrass has purple bands or chevrons on the leaves. Barnyardgrass often has awns or bristles at the end of the spikelets. Both respond the same to herbicides.

Red sprangletop, Leptochloa filiformis, and Mexican sprangletop,Leptochloa uninervia: Red sprangletop is in general a lighter green color and has a finer seed head than Mexican sprangletop which is darker green or gray and has a visibly coarser seed head.

Both form clumps or crowns that often survive through the winter months. Each is fairly tolerant to Poast, sethoxydim, and Fusilade, fluaziflop, but are controlled with high rates of Select, clethodim.

Field sandbur, Cenchrus paucifloru, and Southern sandbur, Cenchrus echinatus, are equally miserable weeds found only in sandy soils and are fairly easy to distinguish. Field sandbur has thinner, gray-colored leaves and yellowish burs that are longer than broad. Southern sandbur has darker and broader leaves and fatter red-colored burs. Southern sandbur has a more compact seed head with distinctly more burs than the southern sandbur. Both are fairly tolerant to Poast, sethoxydim, Select, clethodim, and Fusilade, fluaziflop.

Southwestern cupgrass, Eriochloa gracili, and prairie cupgrass, Eriochloa contracta, are fairly easy to distinguish in the field. Southwestern cupgrass is a wider-leafed grass in the desert. Prairie cupgrass leaves are less wide and are hairy.

Southwestern cupgrass is more branched than prairie cupgrass. The ligule is shorter and less prominent. The branches are longer and fewer on prairie than on the southwestern. Both respond the same to most herbicides.

Green foxtail, Setaria viridis, and yellow foxtail, Setaria glauca, typically form clumps, produce plenty of seed, and stand more upright than most other summer annual grasses.

These foxtails are not difficult to distinguish in the field. Green foxtail has a darker greenish or brown seed head compared to yellow foxtail. The leaves of the yellow plant are generally longer and have more bristles (5-20) per spikelet than the green plant which typically has three or less darker colored bristles. Both respond the same to most herbicides.

Contact Tickes: (928) 782-3836 or btickes@ag.arizona.edu.