|
|
A heatwave gripped Wisconsin and much of the United States this week. Daytime highs soared above 90 degrees across the state and were the hottest of the summer so far, while heat index values exceeded 100 degrees. The steamy conditions along with the return of smoke from wildfires in Canada prompted the Department of Natural Resources to issue an early-week air quality advisory, the 14th advisory for particle pollution so far in 2023 and the most in a single year Wisconsin has recorded in the last decade.
As a heavy summer haze hung over urban and rural areas, corn and soybean development continued at slower than average pace. Corn silking was 25 percent complete at the start of the week, one day behind last year and five days behind the five-year average. For the state’s soybeans, 57 percent of the crop has bloomed, two days behind last year and three days behind the average.
Although some crops have benefitted from recent sporadic rainfall, many areas remain dry. The July 27 U.S. Drought Monitor map shows severe drought (D2) has expanded in northwest and west-central Wisconsin, with some expansion of extreme drought (D3) in the southern areas, including most of Sauk, northern Iowa, and northwestern Dane counties.
__________________________________
|
|
Emergence of western bean cutworm moths increased abruptly with the high temperatures of the past week. DATCP’s monitoring network of 43 traps captured a very high total of 3,431 moths (80 per trap average) during the week of July 21-27, which is more than double the 1,518 moths (35 per trap average) collected the week before. Thirteen of the 43 traps registered 100 or more moths and four traps captured over 250 moths. These elevated counts indicate the annual flight has peaked across much of southern Wisconsin and in areas near La Crosse.
According to the western bean cutworm degree-day model, peak moth activity, or 50% emergence, coincides with the accumulation of 2,704 degree days (modified base 38°F). Moth emergence currently ranges from 50-75% complete across far southern Wisconsin and is approximately 25% complete in the central counties south of Highway 10. Near Wausau and northward, 25% of the population should emerge next week and the flight is expected to peak August 6-12.
The window of peak moth activity now open also signifies the peak egg laying period for western bean cutworm. The opportunity to scout for egg masses has likely passed in the south but will remain an option through the second week of August in central and northern Wisconsin. For these areas, the bulk of this year’s western bean cutworm eggs will be laid in pre-tassel/pollinating corn in the next two weeks. Scouting entails checking 20 consecutive plants in five separate areas of the field for egg masses laid on the upper surface of the top leaves. The treatment threshold has been met if egg masses or small larvae are found on 5% or more of the plants. |
|
 __________________________________
|
|
In June 2023, DATCP staff observed symptomatic rhododendrons during routine inspections that led to 15 confirmed detections of Phytophthora ramorum at a licensed Wisconsin nursery dealer. The infected plants had been imported from Oregon earlier this spring. These detections were discovered on 12 ‘Holden’ rhododendrons, one ‘Nova Zembla’, one ‘Purple Passion’, and one ‘Maxecat’ rhododendron. All interceptions of P. ramorum-infected plant material were properly contained, disposed of, and the nurseries were disinfected as required by USDA regulation.
While DATCP has occasionally intercepted P. ramorum on imported nursery stock, to date P. ramorum has never been detected on plants in the Wisconsin landscape. DATCP first confirmed the detection of P. ramorum at a Wisconsin nursery in 2019. This was after receiving notification that a Washington nursery had shipped over 4,000 rhododendrons and 400 azaleas potentially infected with P. ramorum to two Wisconsin nurseries, which then redistributed them to 59 nursery locations. Follow-up inspections at those nurseries that same month resulted in the collection of a single symptomatic rhododendron that tested positive for P. ramorum. The nursery promptly destroyed all host plants, soil, and pots within a four-meter radius of the infected rhododendron.
Early detection of this pathogen is key to protecting Wisconsin green industries. Home gardeners or horticulture professionals who suspect their plants may be infected with P. ramorum are urged to contact the University of Wisconsin–Madison Plant Disease Diagnostics Clinic at (608) 262-2863 or bdh@plantpath.wisc.edu. Licensed nursery growers with plants showing symptoms consistent with P. ramorum infection are asked to contact DATCP’s nursery program at (608) 516-7617 or DATCPnursery@wisconsin.gov. |
|
 __________________________________
|
|
|
The summer codling moth flight is underway in Wisconsin. Several cooperating apple orchards are reporting very large moth flights, suggesting that pressure from second-generation larvae may be high next month. High codling moth pressure is indicated by a weekly count of > 5 moths per trap for orchards not using mating disruption (non-MD) and > 2-3 moths per trap for orchards using mating disruption (MD). Counts this week ranged as high as 37 moths per trap, with eight locations reporting above-threshold counts.
For non-MD orchards with high codling moth counts in the range of 5-37 moths per trap, second generation pressure will likely be heavy and applying first controls at 250 degree days from the summer biofix is recommended. In contrast, orchards seeing low moth pressure as the second flight begins (< 5 moths per trap for non-MD and 0-1 moths per trap for MD) can delay treatment until 350-400 degree days from the summer biofix.
Codling moth traps should be checked regularly throughout August to determine the need for late-season control. An insecticide application is not necessary if trap counts do not exceed the economic threshold of five moths per trap per week. Growers are reminded to rotate control products between generations and review pre-harvest intervals before making an application.
Apple maggot emergence also increased this week at several orchard monitoring sites. Economic counts were reported from 11 of 26 reporting locations. Peak emergence of adult flies is approaching and oviposition on apples can be expected throughout August. Apple growers should continue to apply sticky coating to traps each week (or as needed) and maintain apple maggot controls as long as counts exceed the following economic threshold:
- One fly per trap per week for unbaited traps
- Five flies per trap per week for baited traps
 Apple maggot flies | Lucy Kailhofer, The Little Farmer
|
|
 __________________________________
|
|
|
|
