The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz. released Jan. 23, 2013.

Seedcorn maggots in spring melon plantings

By John Palumbo, UA research scientist and Extension specialist

The probability of certain insects occurring when environmental conditions and management practices are favorable can be quite high.

The seedcorn maggot (SCM) on spring melons crops is a good example. SCM can cause significant stand reductions in spring melons and other large-seeded crops due to larvae feeding on germinating seed, roots, and even the stems.

If SCM populations are high, replanting parts or all of an infested field is often necessary. Not only is this an inconvenience to the grower, but replanting is expensive and can disrupt harvest schedules.

When maggots are found infesting the soil during stand establishment, there is usually nothing the grower can do. Avoidance of the problem is the most effective way of preventing stand reductions (check out this link - Seed corn maggot 2013).

The weather plays a major role in determining the damage potential for SCM. Melon stands are more susceptible to SCM during wet, cool spring weather when seed germination is slowed or delayed. These conditions give SCM a chance to develop in the soil and attack the seeds before emergence.

The desert cropping system also plays a key role. Melon crops followed by produce are often attacked because SCM is attracted to fields with high levels of decomposing organic matter. This includes heavy plant residue after the harvest of the previous lettuce or cole crop, plus applications of manure prior to planting.

Growers should not plant melons into fields under these conditions. If growers do plant, it is wise to use a preventative insecticide applied at planting to minimize the impact from SCM and give seedling stands a fighting chance.

A few alternatives are available which have shown activity against SCM and may be practical for SCM management in spring melons. Read more about this via this link - SCM Control on Cantaloupes 2012.

Click this link to listen to John.

“Remember, when in doubt - scout.”

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

Low temperatures and plant disease

By Mike Matheron, UA Extension Plant Pathologist

The recent dry weather pattern in the Desert Southwest has greatly reduced the progression of diseases including downy mildew which thrive when relative humidity and free moisture are abundant.

Unfortunately, the same dry weather pattern subjected crops in the region to freezing temperatures earlier this month. The temperatures damaged plant tissue which can serve as colonization sites for some biological pathogens of these crops.

Lettuce drop, for example, caused by Sclerotinia minor and S. sclerotiorum, often begins on senescing lettuce tissue. It does not matter to the fungi whether the tissues are senescing due to natural old age or due to damage resulting from a freeze event.

Additionally, microorganisms which normally would not infect healthy vegetable crop tissue can sometimes invade injured tissue and cause additional damage. Crops that have sustained freeze damage should be monitored carefully in the weeks ahead for the appearance of disease symptoms caused by these opportunistic microorganisms.

In a broader sense, some plant diseases or disorders can be caused by non-biological agents and as such do not require a living pathogen.

Symptoms of these abiotic or noninfectious diseases can result from a variety of causes, including low or high temperatures, excessive soil moisture, low or high light intensity, air pollution, mineral deficiencies and excesses, and excessively acid or alkaline soils.

In most cases, these abiotic diseases can be followed by a secondary invasion by a biological plant pathogen.

Click this link to listen to Mike's Update.

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

Impact of lettuce herbicides on wheat

By Barry Tickes, UA area agriculture agent

Wheat is commonly grown following lettuce treated with soil active herbicides. The most commonly used lettuce herbicides are Balan (benefin), Kerb (pronamide) and Prefar (bensulide).

These are root and shoot growth inhibitors which affect grasses. Slight and temporary injury to wheat is not uncommon. Yield loss is rare.

Wheat is a fairly large-seeded grass which is vigorous enough to overcome some injury.

Two herbicides - trifluralin (Treflan) and pendimethalin (Prowl) - have this same mode of action and are registered for wheat in some states. Where trifluralin is used, wheat is normally planted below the treated soil. Pendimethalin is used in the Southwest Desert on wheat after establishment and a good root system is developed.

All lettuce herbicides are normally applied during crop establishment and have at least three to four months to dissipate. The persistence of Balan, Kerb, and Prefar is variable but is normally two to six months.

When these herbicides are applied in a band, it is possible to see some stunting in the band at the early stages of the wheat crop. Wheat normally outgrows this.

Click link to listen to Barry's Update.

Contact Tickes: (928) 580-9902 or btickes@ag.arizona.edu.

Assassin bug eclosion

Assassin bugs (Reduviidae family) play an important role in biological control. This predator feeds on a wide variety of insects including caterpillars, whiteflies, lacewing, and aphids. A very common genus found in the Desert Southwest is Zelus.

Check out the video Assassin Bugs Top the Food Web (Vandervoet, Ellsworth, and Naranjo).

The next video shows the eclosion of a Zelus egg mass. This is a five-hour video taken by Ta-I Huang at the Yuma Agricultural Center reduced to about three minutes. Check out the video with this link - Assassin Bug Eclosion.