Downy and powdery mildew are caused by the plant pathogenic fungi Bremia lactucae and Erysiphe cichoracearum, respectively. Cool and moist environmental conditions favor development ofdowny mildew, while warmer and dry weather is conducive for development of powdery mildew. Potential new fungicides were evaluated for management of these diseases in 1996. Both downy and powdery mildew developed in the test plots. All tested materials significantly reduced the severity of downy mildew compared to plants not treated with a fungicide. Compared to nontreated control plants as well as some tested materials and rates, significant reduction of powdery mildew was achieved with Azoxystrobin 80WDG + Latron B-1956, BAS 490 02F, Ciba G /MZ + Mancozeb 75DF, Dithane 75DF + Latron CS-7, Propamocarb 6EC (high rate), R11-7281 2F + Larron CS-7, and Microthiol 80WDG.

Three new insecticide chemistries (Alert, Success and Confirm) were evaluated and compared with standard chemistries for residual activity to beet armyworm in lettuce. Lettuce was treated in the field with the insecticides and left for 0, 3, 5 and 7 days. Leaves from treated plants were then brought into the laboratory where second instar beet armvworms were reared on them. Mortality was estimated 5 days after the worms were placed on the leaves. Bioassay were conducted at the thinning, heading, and harvest stages of lettuce. Under high temperature and light intensity, only Alert and Confirm provided the best residual control of beet armyworm, exhibiting good activity for about 3 days after application. Success had better residual activity than Lannate, and both were better than Xentari. Under cool temperatures and low light intensity conditions, Alert, Confirm and Larvin exhibited good activity for at least 5 days following an application, (7 days or greater for Alert and Confirm). Lannate and Xentari both had greater residual activity late in the season, but were not as effective as Alert, Confirm or Larvin. Late season activity of Success did not appear to differ much from early season observations, and did not appear to provide more than 3 days residual activity.

Provado insecticide (imidacloprid) was compared to Admire and other standard insecticides for management of aphids in head lettuce in Yuma 1995 and 1996. Foliar applications of Provado appear to provide an alternative method of controlling aphids on lettuce comparable to prophylactic applications of Admire. The prevention of aphid colonization in lettuce heads with Provado may depend greatly on the timing and frequency of applications before harvest occurs. These studies and other studies on spinach suggest that more than one application of Provado will be necessary to adequately suppress aphid contamination in heads. The label suggests that applications be timed 5-7 apart. Our data tends to support this recommendation. Furthermore, timing applications should be based on days to harvest, level of aphid colonization and duration of aphid migration.

In western Arizona, the incidence and severity of lettuce drop, caused by the fungus Sclerotinia sclerotiorum, can be significant during February, March and April. During 1986 a field trial was established to test new fungicides for disease control. Disease severity in the inoculated lettuce planting was significantly reduced by Baycor, Spotless and CGA-449, as well as the registered fungicides Ronilan and Rovral. Further testing of Baycor, Spotless and CQA-449 will be performed next year.

Tepary beans perform better than common beans under drought conditions. The mechanism of drought tolerance in tepary bean seedlings was explored by determining the water potential, osmotic potentia4 relative water content and level of free sugars and concentration of K ions within expanding leaves. Two week old seedlings were subjected to a gradual water stress with sorbitol solutions exhibiting OP values of -0.19 MPa and -0.47 MPa. Tugor remained constant whereas WP, OP and RWC declined following the stress treatment. Osmotic adjustment (0.4) occurred in each treatment but the contribution of sucrose and fructose to OA was minor. Some sorbitol was translocated to leaves and contributed to OA. The K ions did not contribute to the OA. A significant decrease in cell size was observed

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No description available.

This report focuses upon our efforts to evaluate the effect of sustainable versus conventional fertilization practices on subsequent populations of soil-borne pathogens on lettuce roots. The different fertilization treatments included conventional fertilizer, composted cow manure, and a biological soil conditioner. Near plant maturity, lettuce roots were collected from the field and the populations of Pythium and Fusarium were determined. The lowest population of both of these pathogens was found in the plots fertilized with composted cow manure, while the highest levels of Pythium and Fusarium were detected in the plots treated with conventional fertilizer. Further field studies are planned to confirm these initial findings. Of the two pathogens assayed, Pythium is of greatest concern because of its ability to destroy roots and reduce plant growth and vigor. Species of Fusarium are commonly found in soil and on plant roots and usually do not cause damage to plants unless the plants are under stress.

Leaf drop of lettuce, caused by the plant pathogenic fungi Sclerotinia sclerotiorum and S. minor, is found every year in some lettuce fields in Arizona. When environmental conditions are favorable, disease incidence and resulting crop loss can be significant. During the 1989 -90 lettuce season in western Arizona, different fungicides and rates of materials were evaluated in the field for disease control Ronilan and Rovral, the two fungicides currently registered for use on lettuce for control of Sclerotinia leaf drop, provided significant disease suppression and increased yields at all rates tested. Bravo and Botran did not control the disease.

A field study was conducted at Yuma in 1990 to examine the efficacy of several biological insecticide formulations on beet armyworm in seedling lettuce. After a single application at thinning, none of the insecticides adequately reduced larval populations below damaging levels. Reductions in plant stand by larvalfeeding were significantly lower in plots treated with Lannate, Javelin, Biobit and Dipel. Lettuce seedling densities were reduced greaterthan 80% in untreated plots.