Imidacloprid is a new, chloronicotinyl insecticide currently being used to control sweetpotato whitefly (Bemisia tabaci Genn, also known as silverleaf whitefly, Bemisia argentifolii Bellows and Perring). Large growth and yield increases of cantaloupes (Cucumis melo L.) following the use of imidacloprid have caused some to speculate that this compound may enhance growth and yield above that expected from insect control alone. Greenhouse and field studies were conducted to evaluate the growth and yield response of melons to imidacloprid in the presence and absence of whitefly pressure. In greenhouse cage studies, sweetpotato whiteflies developed very high densities of nymphs and eclosed pupal cases on plants not treated with imidacloprid, and significant increases in vegetative plant growth were inversely proportional to whitefly densities. Positive plant growth responses were absent when plants were treated with imidacloprid and insects were excluded. Results from a field study showed similar whitefly control and yield responses to imidacloprid and bifenthrin+ endosulfan applications. Hence, we conclude that growth and yield response to imidacloprid is associated with control of whiteflies and the subsequent prevention of damage, rather than a compensatory physiological promotion of plant growth processes.

Powdery mildew of cantaloupe in Arizona is caused by the plant pathogenic fungus Sphaerotheca fuliginea. The disease is found in melon fields each year; however, the incidence and severity of the disease is quite variable. Disease development is favored by low relative humidity, moderate temperatures, and succulent plant growth. Potential new fungicides were evaluated for disease control in a field trial conducted in the spring of 1994. In this study, Rally and Reach provided the highest level of disease control and highest percentages of marketable fruit when compared to untreated cantaloupe plants.

Most experimental treatments effectively reduced Bemisia tabaci [sweetpotato whitefly (WF) also known as silverleaf WF, B. argentifolii] adults and eggs in cantaloupes relative to the untreated check at 6 days after treatment of each of five applications. Acephate (Orthene®), buprofezin (Applaud®), bifenthrin (Capture®), endosulfan, fenpropathrin (Danitol®), naled (Dibrom®), and pymetrozine(CGA -215944, Ciba) treatments had the fewest adults and eggs. Insect growth regulator (IGR) materials in combinations, pyriproxyfen (S-71639, Valent) and fenoxycarb (Ciba),were more effective in reducing WF relative to the untreated check than when applied alone. Registered products, Dibrom®, endosulfan, and methamidaphos (Monitor®) were effective in combinations or in alternating applications.

Preemergence herbicide treatments metolachlor (Dual®) and pendimethalin (Prowl®) gave better than acceptable weed control ( >85 %) of prostrate and tumble pigweeds, puncturevine, common purslane, and groundcherry in cantaloupes. Preplant incorporated treatments provided less than adequate control of pigweeds and groundcherry. Bentazon (Basagran®) applied postemergence gave good control of pigweeds but groundcherry control was marginal. Napropamide (Devrinol®), trifluralin (Treflan®), and DCPA (Dacthal (D) caused cantaloupe stand reduction and injury. Bensulide (Prefar®) and Basagran® were safe when applied on cantaloupes.

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Powdery mildew of cantaloupe and other melons occurs every year in Arizona; however, the incidence and severity of the disease is quite variable. This disease, caused by the plant pathogenic fungus Sphaerotheca fuliginea, is favored by moderate temperature and relative humidity, succulent plant growth and reduced light intensity. Potential new fungicides were evaluated for disease management in a field trial conducted in the spring of 1996. All tested products significantly reduced the level of disease compared to nontreated melon plants. In addition to compounds already registered for use on cantaloupe, such as Microthiol Special, Reach, Benlate, Bayleton and Bravo, the list of efficacious nonregistered agrochemicals included Quadris, Procure, BAS-490, and Rally. The possible availability of new disease management tools in the future for powdery mildew of cantaloupe and other melons could enhance our efforts to reduce the development of resistance to these fungicides by the pathogen.

Several experimental insecticide treatments alone or in combinations were evaluated and demonstrated efficacy against Bemisia argentifolii [silverleaf whitefly (WF) also known as sweet potato WF, B. tabaci]. At each rating date following each of four applications, the number of adult and immature WF were reduced relative to the untreated check CGA-215944 (Ciba) treatment combinations were similar at each rating date and significant differences could not be distinguished between the addition of fenoxycarb (Ciba) or CGA-59205 (Ciba). Combinations of insecticides or alternating with insect growth regulators (IGR's) also significantly reduced numbers of WF adults and immatures similar to the standard treatment of bifenthrin (Capture®) plus endosulfan. A single application of pyriproxyfen (Valent) was followed by different treatments [endosulfan followed by fenpropathrin (Danitol®) plus methamidaphos (Monitor®) followed by endosulfan] at each application date. Buprofezin (Applaud®) was combined or alternated with endosulfan at each application and similar reduction of WF was observed. Pyridaben (BASF) did not adequately reduce WF adults and immatures relative to the standard treatment in this test. The Ciba compounds and single or multiple applications of the IGR's, pyriproxyfen and Applaud were highly effective in substantially reducing WF immatures and adults in this test.

In small plot field testing, the new IGR's, buprofezine, pyriproxyfen, and fenoxycarb plus CGA-215944 , offered very good reduction of the WF adults and immature stages for several weeks. Combinations of the new insecticides and alternating weekly applications were effective in minimizing WF season-long. Pyrethroids, bifenthrin and esfenvalerate plus endosulfan treatments, were effective after early applications and nymph counts were elevated after the third application. Oxydemeton-methyl and imidacloprid treatments applied weekly compared favorably with the new chemistries to reduce adults and immatures. Pyridaben applied weekly reduced adult counts relative to the untreated check but immatures increased after the third application.

Clomazone (Command®), bensulide (Prefar®), sulfentrazone, and halosulfuron treatments applied preemergence (PREE) provided very good control of prostrate pigweed (Amaranthus blitoides), lambsquarters (Chenopodium album), and common purslane (Portulaca oleracea) at better than 90% at 5 weeks after treatment (WAT). Halosulfuron was effective in controlling all weeds better than 90% at 7 WAT Carfentrazone was not effective against most of the weeds present in the test but appeared to be safe on cantaloupe. Postemergence (POST) treatments alone did not provide acceptable control of pigweeds but controlled lambsquarters and common purslane at 2 WAT. Halosulfuron and bentazon (Basagran®) applied POST following PREE treatments controlled most of the weeds better than 90% through 7 WAT. Cantaloupe yields were highest with good weed control provided by PREE treatments followed by POST herbicide applications. Basagran at 0.50 lb /A injured cantaloupe after applications but yields were not affected compared to the untreated check. Command, sulfentrazone, and halosulfuron caused cantaloupe injury after PREE applications. Basagran caused substantial crop injury after POST applications.

The postemergence (POST) herbicide treatments did not cause any crop stand reduction following applications. Bentazon (Basagran®) at 0.50 lb AI /A caused marginally acceptable injury on the cantaloupe leaves. At 2 weeks after treatment (WAT), the amount of injury decreased and cantaloupe treated with Basagran at 1.0 lb AI/A showed marginally acceptable injury symptoms. Halosulfuron (Monsanto) at 0.05 to 0.10 lb AI/A caused slightly more injury (10 to 17 %) with increasing rates. Basagran at 1.0 lb Al/A gave good control ( >90 %) of morningglory and was marginal in controlling morningglory at 0.75 lb AI/A Halosulfuron at 1 WAT was marginal in controlling morningglory but improved to give acceptable control at 2 WAT. Fewer and smaller plants were removed by hand-hoeing from Basagran and halosulfuron treated plots compared to the untreated check.