A Florida strain of sweet potato whitefly, Bemisia tabaci (Gennadius), was found to have an expanded range which includes several new food crops. To determine why, we examined how it processes plant nutrients. The amino acid and carbohydrate content of phloem sap from poinsettia and pumpkin and of honeydew produced by the Florida strain were analyzed Honeydews produced by a strain from Arizona feeding on both plants were also analyzed Poinsettia phloem sap contained 15 amino acids; 14 of these were in pumpkin phloem sap. Almost all the same amino acids were in the honeydews produced by the two strains on the two hosts. Carbohydrates in phloem sap and honeydew were common transport sugars, like sucrose. Both honeydews contained trahalulose, a disaccharide not previously associated with insects. Both strains processed phloem sap and honeydew from both plants in the same manner, but the Florida strain produced significantly larger quantities of honeydew; it is therefore assumed to process more phloem sap. Since this strain has access to more phloem sap it also has access to more of the amino acids, which are in short supply in the phloem sap of some plants, allowing it to broaden its range.

Powdery mildew of cantaloupe, caused by the fungus Sphaerotheca fuliinea, is a perennial and often serious disease in Arizona. In 1989, potential new fungicides were evaluated for disease control in a field trial. All tested materials provided significant control when compared to untreated plants. Of the compounds tested only Bayleton currently is registered for use on cantaloupe. Rally, which performed extremely well in this test; should be available for use on cantaloupe in the near future.

Osmotic adjustment is one of the adaptive responses of plant species to salinity, In tepary bean seedlings, salinity led to osmotic adjustment in different parts of the seedlings. The osmotic potential of the leaves increased to 340rnM(-1MPa)in seedlings treated with - 0.75 MPa NaCl. Water and osmotic potential of leaves and proximal parr of the roots were more negative than the controls whereas the turgor potential remained about the same. The osmotic adjustment of the tepary bean may result from the synthesis and accumulation of free sugars and amino acids or the accumulation of inorganic ions within the tissue. A quantitative analysis of the sugars and amino acids from salt stress treated tepary bean seedlings showed that they would contribute only -0.15 MPa to the osmotic adjustment whereas inorganic ions would contribute -0.45 MPa. The sum of these osmotic potentials is -0.6 MPa which is -0.4 MPa short of the observed osmotic values. These results suggest that additional substances also contribute to the osmotic adjustment of tepary beans.

The Crop Water Stress Index (CWSI) was used to schedule irrigations on Jubilee sweet corn on 12 drip- irrigated plots at the Campus Agricultural Center in Tucson. Irrigations were to be scheduled at 0.15, 0.35, and 0.50 CWSI values to represent a wet, medium and a dry treatment. Actual average CWSI values at time of irrigation were for 0.14, 0.36, and 0.48. There were no significant yield or quality differences for the wet and medium treatments with exception of a greater ear diameter in the wet treatment. Yield and quality significantly decreased for the dry treatment scheduled at a CWSI value of 0.48. Irrigation application totals were 26.4, 24.2 and 18.3 inches for the wet, medium and dry treatments respectively.

A complete factorial experiment using three nitrogen (67, 156 and 245 lbs N/acre) and three water rates (70, 100 and 130% consumptive use) examined the specific management criteria necessary for obtaining optimum yield and quality of drip- irrigated 'Sweetie '82' sweet corn. The crop was planted on 22 February and harvested on 30 May with an 86/50° F heat unit accumulation of 1444. When present, a nitrogen deficiency greatly decreased marketable yield number of marketable ears/plant mean ear weight, ear length and tip fill. Higher moisture rates generally had less effect on yield and quality than did N rates; however, increasing water rates significantly increased marketable yields and plant height. The effect of N and water rates on N and dry matter accumulation and on diagnostic plant tissue testing results for sweet corn are also presented The maximum marketable yield obtained in this experiment was 7.2 tons per acre, using 245 lbs N/acre and 20.5 inches of irrigation water.

Leaf drop of lettuce, caused by the fungus Sclerotinia sclerotionunb is a sporadic but potentially destructive disease in Arizona During the 1988-89 lettuce season in western Arizona, different fungicides and formulations of materials were evaluated in the field for disease control. All tested compounds provided significant disease suppression and increased yields, provided that a sufficient rate of fungicide was applied. Ronilan and Rovral, the two fungicides currently registered for use on lettuce for Sclerotinia leaf drop, were the most effective fungicides in this test, performing significantly better than the two experimental materials. The SODF formulation of Ronilan provided significantly better disease control than the SOW formulation of the same compound.

Infection by lettuce infectious yellows vines was reduced in lettuce treated with stylet oil. There was a difference in the final infection level between treated and untreated blocks and reduced infection in early readings. Yields were slightly better in the treated blocks. It has not been determined if and under what conditions it would be feasible to use this treatment on a practical scale.