Arizona Veg IPM: fall melon pests, plant pathogens, summer annual grass

Arizona Veg IPM: fall melon pests, plant pathogens, summer annual grass

As low desert growers plant fall melons, pest control advisers will likely encounter insects which have the potential to cause serious economic losses to seedling crops during stand establishment. To survive, plant pathogens must deal with high temperatures and the lack of food by employing other tactics. Grass weeds are generally more of a problem during the summer than other times of the year. The common name jewel beetle refers to a large group of scarab beetles in the genus Chrysina.

The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz., released July 25, 2012.

Insect pests at stand establishment in fall melons

By John Palumbo, UA Research Scientist and Extension Specialist

As growers plant fall melons, pest control advisers will likely encounter insects which have the potential to cause serious economic losses to seedling crops during stand establishment.

The insects include flea beetles, crickets (sometimes grasshoppers), darkling and rove beetles, and saltmarsh caterpillars. These insects have chewing mouthparts and can consume large amounts of leaf tissue in a short period of time.

Seedling crops at the cotyledon stage are most susceptible to these pests.

Feeding by large numbers can devour much of the cotyledons or outright kill the small plants. If left uncontrolled, larger seedling plants (2-4 leaf stage) can sustain significant feeding damage on the terminal growing points or newly emerged leaves.

Not only can this feeding stunt plant growth, it can result in the lack of uniformity and maturity at harvest.

Host sources of flea beetle, cricket, and “wooly worm” infestations include numerous summer crops (e.g., sudangrass, cotton, and alfalfa) and a large host of weeds (e.g., purslane). Experience suggests that melons fields planted adjacent to these crops/weedy areas are at a high risk from these seedling pests, particularly from flea beetles.

As these summer host plants are harvested or terminated during the next several weeks, the seedling pests typically move to the next available host crop - lettuce, cole crops, and melons.

Fortunately, there are many registered insecticide alternatives available applied via sprinkler chemigation (i.e., pyrethroids) or foliar sprays (i.e., Lannate, neonicotinoids) to cost effectively minimize the abundance and damage to emerging melon crops.

For more information on insect pests of leafy vegetables and melons at stand establishment, click on this link: Insect Management on Desert Produce and Melons.

Click this link to listen to John.

Remember - when in doubt – scout.

Contact Palumbo: (928) 782-3836 or [email protected].

Plant pathogen survival in the desert

By Mike Matheron, UA Extension Plant Pathologist

Those living in the desert can escape the desert heat by finding refuge in air-conditioned buildings or can obtain food from any number of sources at any time.

On the other hand, plant pathogens have to survive high temperatures and the lack of food by employing other tactics.

A few plant pathogens can thrive at hot temperatures common in the desert during the summer and cause disease on plants growing at that time. However, most others cannot function at temperatures much above 90 degrees Fahrenheit.

To survive inhospitable temperatures or the lack of a feeding host, fungal pathogens often produce thick-walled durable spores or other structures which allow the organism to survive hostile environments in a dormant state.

The visible dark-colored sclerotia produced by the lettuce Sclerotinia pathogens are such structures. Much smaller sclerotia and thick-walled spores facilitate long-term survival of the soil-borne pathogens Rhizoctonia and Fusarium, respectively.

In comparison, bacterial plant pathogens do not have recognized survival structures, but can subsist for some time in a reduced metabolic state on, in, or near living or dead plant tissue.

Virus pathogens also cannot make resistant structures so survival usually occurs in living plants or vectors. These plants can include weeds or cultivated crops that do not express disease symptoms, but serve as sources of virus to visiting insect vectors.

Finally, nematode survival stages can include eggs and certain larval forms. Many of the cultural disease management methods now employed are effective since the methods disrupt the normal survival capability of these plant pathogens.

Click link to listen to Mike's Update.

Contact Matheron: (928) 726-6856 or [email protected].

Summer annual grass identification

By Barry Tickes, UA Area Agriculture Agent

Grass weeds are generally more of a problem during the summer than at other times of the year.

There are more than 25 annual grass species found in the low desert during the summer, although only about 10 are common. Most of these look very similar at early growth stages and identification can be difficult.

There is a tendency to lump species together and call them water grass, jungle rice, barnyard grass, or several other names. There are differences between them, however, and it is important to accurately identify the species at early growth stages.

This is important since many species respond differently to herbicides and have different growth habits.

For example, sprangletop is only controlled by the highest rates of Select (clethodim) and generics of this herbicide. Sprangletop is missed by other selective post-emergence herbicides including Poast and Fusilade. Sandbur is tolerant to all of them.

By the same token, sandbur and sprangletop can overwinter, come back from crowns, and are not controlled by pre-emergence herbicides applied in the spring while most other summer annual grasses die in the winter and the seed can be controlled with herbicides in the spring.

There are six genera and 12 species of summer annual grasses common in the low desert. These include echinochloa (water grass and barnyard grass), leptochloa (red sprangletop and mexican sprangletop), eriochloa (southwestern cupgrass and prairie cupgrass), cenchrus (field sandbur and red sandbur), setaria (green foxtail and yellow foxtail), and chloris (feather finger grass and truncate finger grass).

A related PowerPoint presentation can be found by clicking on Summer Annual Grass ID which contains pictures and descriptive characteristics of each species.

Click this link to listen to Barry.

Jewel beetles in Arizona sky islands

By Ta-I Huang, UA post doc research associate

The common name jewel beetle refers to a large group of scarab beetles in the genus Chrysina which was previously called Plusiotis. The shiny color reflection on the elytra (fore-wing) - mostly green while some are silver or gold – earns the beetle the beautiful name jewel beetle.

This beetle is one of the most attractive insects in the world. The high market value lures many hobbyists and professional beetle collectors worldwide to trap the beetle using mercury vapor lamps and black lights.

There are approximately 100 species of Chrysina beetles around the world. Four species occur in North America - three in Arizona and one in Texas.

Adult beetles emerge during the onset of monsoon season in Arizona sky islands and then disappear in the fall when the temperature decreases.

The beetles overwinter as larval stage (white grub) in the underground, feeding on plant roots and organic matter, pupate in the soil in the spring, and then thousands of adults fly out in summer after a soaking rain brought by the monsoon.

I chose the Santa Rita Mountains as my destination for my first trip of Chrysina exploration. This place is one of the very few locations to see the three Arizona Chrysina species together in one night.

This area is also one of the legendary habitats for bird watching naturalists, but also for beetle collectors.

I set up black and HID lights in one parking area about 5,000 feet in elevation. Two lights were 10 meters apart from each other.

At 8:20 p.m., the first jewel beetle, Chrysina gloriosa, landed on the ground near the HID light. This shiny green-colored beetle with a silver stripe on its back explains why this insect is called the jewel beetle.

In fact, C. gloriosa is the most common Chrysina species of North America found in the mountains of southeastern Arizona, southern New Mexico, and southwest Texas.

Before the beetle arrived, hundreds of other beetles occupied my white sheets under the lights, most of them in the families Cerambycidae and Scarabaeidae.

While I was checking on the first jewel beetle ever in my life, a second species, C. lecontei, arrived. The male C. lecontei is relatively smaller than C. gloriosa (one-inch long), which has a dark green body and red legs, and no silver stripe on the elytra, which makes this species seemly less attractive than C. gloriosa.

Chrysina lecontei’sdistribution in Arizona is as widespread as C. gloriosa but less common in most areas.

Over the next two hours, my HID and black lights were attacked by a crowd of Chrysina beetles, including the 3rd species C. beyeri. This species is the largest jewel beetle in North America (~1.5 inch). The apple green elytra with purple legs match perfectly on this spectacular beetle.

The distribution of C. beyeri is limited to certain mountain ranges in southern-most Arizona including the Huachuca Mountains, Patagonia Mountains, and Santa Rita Mountains.

Limited distribution makes C. beyeri more desirable and mysterious among beetle hobbyists.

During a warm summer night, C. beyeri may come to the black light as abundant as C. gloriosa if it is the right habitat.

Although Chrysina jewel beetles are still quite abundant in Arizona sky islands, the insect is overly collected due to the high commercial value.

Further research on the insect’s biology and ecology should be conducted in the future. Protection for these beautiful insects may be considered.

Listen to Ta-I.

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