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There are around 1,000 acres of fruit tree production in the High Desert near Lancaster, CA. Most of the fruit tree acreage is in peaches and nectarines with some apples, pears, and other tree crops. The most significant problems high desert tres fruit growers face are from the insect pests peach twig borer (in peaches and nectarines) and codling moth (in apples and pears). Currently there are several techniques used to monitor these pests to assess pest pressure and time chemical applications for more effective control.
Integrated pest management is simply a term used to describe a strategy to effectively control a pest through the use of insect monitoring, biological control, and proper timing of chemical applications. Monitoring pest populations and activities through the use of insect trapping and a growing degree-day model has proven to be a useful tool in determining pest pressures. Once pest pressures and flight patterns are determined, growers can more appropriately choose chemicals and time spray applications for better pest control.
The growing degree-day model uses high and low temperatures to predict the activity of the insect. A version of the degree-day model and table can be accessed on the internet via the website http://www.ipm.ucdavis.edu/WEATHER/DDTABLE/peach_twig_borer.html. Use the degree day calculator. Palmdale is the nearest weather station in the degree day calculator. A version of the degree day table can also be found in the UC publication number 3389 "IPM for Stone Fruits". Table 1 summarizes the significant growing degree day accumulation points as they relate to major PTB events in the high desert.
Table 1. Summary table of important monitoring events according to growing degree days.
| Growing Degree Day Accumulation | Event | Local 2002 Event Occur. |
| 50 degree F daily temperatures | Begin degree day accumulation | Late Feb. |
| 300 degree days | Place traps in orchard | Mid-March |
| 400-450 degree days | Expect emergence of PTB | Late Mar.- Apr. |
| Establish first biofix-Consistent # of adults trapped | Begin accumulating degree days from 0 | April 7 |
| 300 degree days after first biofix (50% bloom) | First generation Bt treatment time | April 10-20 |
| 400 degree days | First generation conventional chemical treatment (Success, Imidan, etc.) | May 7 |
| 450-500 degree days after first biofix (70-100% bloom) | Second generation Bt treatment time | Early May |
| 950-1080 degree days | Complete peach twig borer generation | May 31 |
| Establish Second Biofix-Consistent # of adults trapped | Begin accumulating growing degree days from 0. | June 15 |
| 300 degree days | Second generation treatment (colored fruit) | July 1 |
Adult emergence in the spring is dependent upon temperature. Trapping during 2002 showed emergence of PTB in Littlerock occurred around April 7-10th.
To monitor for peach twig borer begin the season by placing traps in your orchard in late February to early March. You can begin accumulating growing degree days when daily average temperatures begin to exceed 50 degrees F and expect to see emergence at approximately 450-550 degree days.
The adult peach twig borer may be identified by its characteristic mottled gray appearance with a long snout like projection from its head. Once you begin to catch peach twig borers consistently, that is two insects per trap for two consecutive days, then begin accumulating growing degree-days. This reference point is often referred to as the "biofix". From this point begin accumulating growing degree-days according to the chart found on the UC IPM web site or in publication number 3389.
From the time of the biofix, treatments may be applied according to a couple of different approaches. The first is an integrated approach involving the use of a biological pesticide called Bt (Bacillus thuringiensis). Bt is to be applied at egg hatch to target the young PTB larvae. However, the efficacy of the chemical is short lived and must be applied at 300 degree days, or 50% bloom, and again at 400 degree days, or approximately 70-90% bloom.
The advantage of the integrated approach is to conserve beneficial insects, such as lace wing larvae and parasitic wasps for biological control of PTB, but moreover it saves the six-spotted thrip and western predatory mite which will suppress spider mites that are problematic during the summer months. The use of conventional organophosphate and pyrethroid pesticides will suppress these beneficial insects, but the integrated approach relies more heavily on beneficial insect populations to control pests. However, the risk for fruit damage with the integrated approach is often higher and a regular monitoring program is usually warranted. Spinosad ('Success') is another useful biological pesticide labeled for peach twig borer that has a longer efficacy than Bt.
If you have any questions regarding using the growing degree day model for PTB or codling moth, trap contacts, current growing degree days, or where to get the UC publication number 3389 "Integrated Pest Management for Stone Fruits", you may contact UC Cooperative Extension in Lancaster at 661-723-4483. The web site www.ipm.ucdavis.edu is a great resource.