The residual activity of insecticides to second instar citrus thrips was measured on lemon foliage in 1998 and 1999. Dimethoate, Agri-Mek and acetamiprid provided only knockdown control of thrips, dropping to <70% mortality by 3 days after treatment (DAT). Baythroid performed slightly better, providing about 95% mortality 3 DAT during three of the evaluation periods, but by 7 DAT was giving about 75% mortality. Alert, Carzol, and Success provided the longest residual activity, lasting 7 to 14 DAT. Residual activity in general appeared to be greater in the May and June evaluation, relative to the April evaluation. The apparent shorter residual activity under cooler condition in April 1998 is not understood but maybe due to a difference in the physiological nature of the leaves earlier in the season.

Under low citrus thrips pressure and cool temperatures, Alert, Baythroid, Carzol, Success and Acetamiprid applied at petal fall were all effective control agents. Mid-season applications of Baythroid and Danitol were also effective but appeared to be slightly inferior to Success and Alert in residual control. Despite the prolonged blooming and petal drop period experienced during this trial, plots receiving pre-petal fall applications of Acetamiprid did not produce higher quality fruit than treatments where applications began following petal fall. The fact that thrips densities were low during this period may be the reason. Before pre-petal fall insecticide applications can be deemed useful and economically justifiable, evaluations must be made at higher thrips infestation levels.

Three small plot efficacy trials were conducted evaluating different insecticide rotation regimes using commercially available insecticides and the effectiveness of new insecticide chemistries to control citrus thrips. Because of its long residual activity, and ability to control post- application egg hatches, Carzol appears to be the product that best fits the petal fall application window. Agri-Mek, Baythroid, Dimethoate or Vydate are probably good follow -up insecticides. However, Agri-Mek and Baythroid will probably provide greater control, especially under hotter conditions. If temperatures are cool, Agri-Mek looks good at reduced rates. The best insecticide for subsequent applications depends on temperatures and what was previously applied. Avoid making back -to -back applications of the same materials, and Dimethoate or Vydate applications should probably be followed by Carzol to catch post- application egg hatches. Overall, Vydate appears to be very similar to Dimethoate in efficacy and residual activity, while Baythroid appears to be slightly better. Although the addition of Lannate to Dimethoate does slightly enhance thrips control, the additional cost probably does not justify the tank mix. Of the new chemistries (Alert, Success, Ni-25, and M-96-015) evaluated, Success and M-96-015 appeared to offer the best fruit protection. However, M-96-015 does not appear to be very effective in killing the thrips, but is very effective in repelling them. Also, M-96-015 will need to be applied at a high gallonage, i.e. 500 gal/A. None of the new products tested appear to fit the petal fall application window very well. Ni-25, Alert and Success appear to lack the residual activity of Carzol, and M-96-015 should not be used as a clean-up material but preventively following Carzol at petal fall.

Two small plot efficacy trials were conducted evaluating different insecticide rotation regimes using commercially available insecticides and the effectiveness of new insecticide chemistries to control citrus thrips. Under the consistently cool conditions experienced during the first four weeks of the trial, Dimethoate, Success, Baythroid, Agri-Mek, Vydate and Carzol all of the offered adequate control and would fit well in the petal fall window. This is in contrast with previous years experiences when high temperatures within a week of petal fall would result in all treatments except Carzol requiring a re-treatment within ten days. All of the rotation schemes evaluated required three insecticide applications to get through the season, and did not appear to be greatly different in controlling thrips and producing high quality fruit under the environmental conditions experienced. However, the Dimethoate - Success - Baythroid rotation scheme was most cost effective. When temperatures were in the 70's to low 80's, Dimethoate and Vydate offered about three weeks control, Success, Carzol, Baythroid and Agri-Mek all offered about four weeks control. When temperatures were in the mid to upper 80's and low to mid 90's, Success provided about three weeks control while Carzol didn t require re-treatment for 4 weeks. Under these same temperature conditions, Dimethoate and Vydate gave about 7 to 12 days control, and Agri-Mek provided 12 to 14 days of control. Other than the one control failure with Baythroid, under warmer conditions, it provided about seven days control. In the experimentals test, AZEXP1 appeared to offer knockdown activity at temperatures less than 90 F, and only suppression at higher temperatures. AZEXP2, appeared to be a viable citrus thrips material, with activity similar to Success and Carzol. The knockdown activity of M96 appeared to be enhanced by including Dimethoate or Carzol, but will require multiple applications to achieve the level of repellency experienced in 1997.

New chemistries (Alert, Success, Fipronil, Ni -25, Nexter, Danitol and Baythroid) were evaluated and compared with standard chemistries (Agri-Mek, Dimethoate and Carzol) for control of citrus thrips in lemons grown in the Yuma area. Additionally, Success was compared to Carzol in a large plot commercial demonstration. Under cool, early season conditions, all products appeared to offered good thrips control. However, under warmer conditions, Nexter, Danitol, Baythroid and Dimethoate appear weak. Among the new insecticides, Success and Fipronil appear most efficacious. Alert also appeared to have good activity at the high rate, but appeared to offer shorter residual control than Fipronil or Success. Fipronil was the only new product tested that flared mites. However, rotating sulfur into the Fipronil applications appeared to help prevent flaring. Growers can expect Baythroid and Danitol to behave similarly to Dimethoate for efficacy and residual control. Under commercial conditions, Success provided thrips control equivalent to Carzol at 1.38 lbs-ai/A.

A small plot efficacy trial was conducted evaluating thrips control with Dimethoate, Baythroid, and Success at rates of 4, 6, and 9 oz/ac, and tank mixes of the low and medium rates of Success with Dimethoate or Baythroid. Based on a 10% fruit infestation threshold, Dimethoate required three applications while the other treatments required two applications to achieve season long thrips control. However, when evaluating the treatments based on a cost effectiveness index, none of the tank mixes or Success at 9 oz./ac were economically advisable. The most cost effective treatment was Success at 4 oz/ac, followed by Success at 6 oz/ac, Dimethoate, and Baythroid.

Commercial and University citrus groves were sampled over a two year period in an attempt to develop mathematical models capable of predicting fruit scarring based on the population of immature citrus thrips on susceptible fruit. Five predictive models were derived. One model correlated used citrus thrips populations from fetal fall to 2.0 in. diameter fruit. While in the other models, thrips populations were divided into four distinct fruit size cohorts. Four of the five models were statistically valid. Based on these models, lemons ½ in. in diameter, should be treated with insecticides when the number of immature CT reaches 1.5 per 10 pieces of fruit. While fruit > ½ should be treated if immature CT reach or exceed 2.0 per 10 fruit.

Insecticides were evaluated for their efficacy to citrus mealybugs on lemons at three spray gallonages, 60, 240, and 600 gallons per acre. None of the products tested exhibited any activity at 60 or 240 gallons per acre. At 600 gallons per acre, Lorsban at 6 qt/A + NR-415 oil at 1.4% v/v, Supracide at 2 pt /100 gal + Kinetic at 0.25% v/v, and Applaud at 2.0 lbs -ai/A + NR -415 oil at 1.4% v/v all demonstrated the best activity. Provado at 0.1 lbs-ai/A + NR-415 oil at 1.4 %, Danitol at 0.4 lbs-ai/A + Lorsban at 4 qt/A + NR-415 oil at 1.4% v/v, and Nexter at 0.3 lbs-ai/A + NR-415 oil at 1.4% v/v showed good activity. Weaker treatments included Agri-Mek at 10 and 20 oz/A, Knack and Difenolan. For maximum control, growers should treat before the fruit is heavily infested, and use high gallonages of spray solution at a high pressure, the spray must penetrate the waxy coating to achieve activity. If applicable, a spray oil should be included to help break up the wax. However, if Supracide is used, use a high rate without oil.

Lemons appear to be most susceptible to damage by citrus thrips from petal fall until they reach 1.0 inch in diameter. Correlation analysis suggests that fruit greater than 1.0 inch in diameter may not be highly susceptible to thrips scarring and thus may not require protection. 1f this relationship can be verged with additional data, late- season thrips sprays may be avoided.

When applied early-postemergence, Milestone at 0.75 and 1.0 lbs-ai/A provided excellent control of summer annual grasses and broadleaf weed for as long as 4 months, equivalent to Karmex. Princep and Krovar also provided good weed control but appeared to offer slightly shorter residual against some broadleaf species. Solicam, although it provided good weed control, particularly of the grasses, was the weakest material evaluated in this trial. Although Karmex is notorious for causing crop injury on the sandy soils of the Yuma Mesa, we did not detect any injury from this herbicide or any others in this trial.