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

• Soil solarization

By Mike Matheron, UA Extension Plant Pathologist, Yuma Agricultural Center, Yuma

Summer is upon us and temperatures in the desert are sizzling. Although the summer heat may not be appreciated by desert dwellers, it is the perfect time for soil solarization.

This is accomplished by covering moist soil with clear plastic and allowing the sun’s energy to heat the soil to levels lethal to many plant pathogenic fungi. The plastic conserves soil moisture and retards heat loss.

In field solarization trials conducted from 2004-2007 in Yuma, the average temperature of soil at a depth of two inches during a one-month summer solarization period was 113 F compared to 102 degrees for non-solarized soil. The average peak afternoon temperature in solarized soil during the trials was 128 degrees.

The solarization trials were conducted in soil naturally infested with the lettuce Fusarium wilt pathogen. The incidence of the disease in a subsequent planting of lettuce was reduced from 42 percent to 91 percent compared to disease levels in non-solarized plots.

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

• Purslane

By Barry Tickes, UA Area Agriculture Agent, YAC, Yuma

Common purslane, Portulaca oleracea, is one of the most troublesome weeds in vegetable crops. It is also a nutritious leafy vegetable.

Common purslane is widespread in the desert Southwest but is also on the list of “Arizona prohibited noxious weeds” which means it is prohibited from entry into the state.

Common purslane is consumed in Mexico (Verdolaga), Europe, and Asia. It contains more Omega 3 fatty acids than other leafy vegetables. It also contains vitamins A, B, and C plus dietary minerals.

Common purslane is often lumped together with horse purslane although the two are in different families. Common purslane is in the Portulaca family while horse purslane is in the Trianthema or Carpetweed family.

In lettuce, purslane is often controlled during ground preparation with chemicals or tillage. Timing is important with these techniques.

Purslane grows rapidly. One plant can produce thousands of seeds. The seeds can germinate in 12 hours after receiving moisture in August and September. Germination can occur in January and February in three to seven days.

The stems are very succulent. Unless they are killed and desiccated, the stems can re-root at the nodes. Tillage that fails to completely desiccate the plants can spread the weed rather than eliminate it.

Herbicides to kill purslane during ground preparation include contact herbicides (Gramoxone, Aim, and ET) and systemic (glyphosate) herbicides. Results can range from zero to 100 percent depending upon the weed size, rate, and adjuvant used at the application time.

Contact herbicides can provide near 100 percent control when Purslane is less than two inches in diameter and less than 50 percent control when the weed is larger. This is especially true with Aim where control can drop from excellent to poor in three to five days.

Purslane has a thick waxy cuticle. An adjuvant is needed with these herbicides to help penetrate into the leaves and stems. A non-ionic surfactant helps spread the herbicide and helps it stick while crop oil concentrates help break up the waxy layer.

The time of day of the application can also be important. In morning hours, the leaf pores are open, new growth is occurring, and the plant is more sensitive to herbicides than the middle of the day when the plant is conserving water and energy.

There is a wide range of herbicide application rates to control purslane during ground preparation.

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