Utah Pests News Fall 2007

New Utah Pests Fact Sheets:

Marketing the Lab

2007 Commercial Orchard
Monitoring Re-Cap

 Before discussing the pest activity for the summer of 2007, we need to cover the weather, since it is such a “hot” topic right now. Here are just a few Utah stats for the hottest summer on record to blow you away:

• July was the hottest month on record in Salt Lake City with 25 days of 95 degrees F and over, and the warmest day at 105 degrees. 
• The hottest temperature ever recorded (unofficial) in Utah was on July 4, just south of St. George, at 118 degrees (previous record was 117 degrees in 1985).
• On July 6, St. George never dipped below 92—another record. 
• April was the third driest April on record. 
• During the months of March through August, 306 records were set for daily maximum temperature (113 in March, 35 in April, 61 in May, 25 in June, 47 in July, and 25 in August). Almost as many record high minimums were also set.

Basically, it was a hot, dry summer with some tumultuous storms thrown in the mix. Although the dry weather kept many diseases at bay such as apple scab and powdery mildew, and the trap catch for several orchard insects were similar to past years, other problems were not as you might expect.

Insect Activity

This was a successful year for Utah’s commercial orchardists who use mating disruption as a codling moth management tool. (This method saturates the orchard with pheromone so the males cannot find the females.) Damage incidence and trap catch numbers were far lower than in recent years. We believe the reduced damage is a combination of diligent management practices over several years, and possibly a reduced overall codling moth population size. We cannot speculate on any specific reasons as to why the codling moth population would be lower, except to say that several years’ worth of mating disruption has played a large roll.

Codling Moth Biological Activity/Predictions

The table above shows the dates for 9 of the past 11 years of the first codling moth flight for one orchard in Utah County. For that same location, this year’s date of first flight for 2007 (also known as a biofix) was April 28, which is not too far off the norm, especially when compared to 2004. However, the months of May-August were significantly hotter than those in 2004. In fact, the number of growing degree days (which measures heat accumulation based on daily max and min temperatures) by August 31 was 2852 in 2007 versus just 2482 in 2004.

What does this mean? It means lots of moths have been able to reproduce very quickly. As the temperatures stay warm (especially minimum daily temperatures), the length of the insects’ life cycle shortens. Typically, northern Utah sees two full generations of codling moth and a partial third generation (meaning that only a small portion of the larvae from the second generation pupates. The remaining larvae enter into a resting phase–diapause–for the winter.) However, this year we saw a full third generation in many locations, including Salt Lake, Tooele, Weber, and Box Elder counties, and parts of Utah County.

Because the majority of the larvae in this third generation will be entering diapause, we can probably expect a greater population of moths at the start of the 2008 season.

Trap catch numbers for peach twig borer were average. Damage, however, including shoot strikes and fruit entries, were down from last year. Some orchards in Box Elder County, where there is high twig borer pressure, saw similar damage to last years’ crop.

Fire blight reared its ugly head in many areas of northern Utah this season, with extensive damage in localized areas. One could not have predicted this based on the dry spring; however, only one or two rainfall or "wetting" events at the right temperature are all it takes. There was a heavy rain on May 3 and 4 during late bloom. Where present, existing fire blight cankers had already begun to "ooze" bacteria by this time, and so the rain spread bacteria throughout those orchards, causing numerous floral infections. A second heavy, windy rain on May 23 spread more oozing bacteria from the floral infections to tender young shoots.

Another reason for the wide-spread disease incidence has to do with the susceptibility of the host tree. The most susceptible trees are currently the most in-demand apple varieties today: Fuji, Jonagold, Gala, etc. Resistant varieties can still get infections, but the bacteria are stopped quickly in their tracks.

Finally, there are several colonies ("isolates") of fire blight bacteria that have developed resistance to the antibiotic treatment of choice, streptomycin (strep). As the use of strep increased the last several years, the population of bacteria that could withstand it also increased. Growers were forced to use alternative antibiotics that are unfortunately not as strong a preventative treatment as streptomycin.

Not surprisingly, there were localized outbreaks of both aphids and spider mites across northern Utah orchards on all fruit crops. The mites thrive in heat, so that was to be expected.

The incidence of coryneum blight (or shothole—a disease of peaches and cherries) was reduced significantly this year due to the dryer, hotter weather and growers’ diligent management practices.

Box Elder County Agriculture Agent Mike Pace reported an odd outbreak of boxelder bugs on peaches (shown at left). Some fruits had over 50 bugs feeding on them, rendering the fruits unmarketable. According to Pace, it has been about 5-6 years since seeing this level of activity.

All in all, it was not such a bad year for our fruit growers. The tart cherry and early peach harvests were slightly reduced from last year, while the apple and late-season peach crops are predicted to be heavy. With diligent IPM pest management practices and optimal watering and nutrition, Utah orchardists have given us fruit-lovers some tasty treats to devour.

-Marion Murray, IPM Project Leader