MSU Extension

Weather

Last week started cool with Monday’s (May 3) low near freezing. Lows rose into the 50s for the rest of the week. High temperatures were generally in the mid-70s. No rain fell last week and soils were beginning to dry. Rain fell Monday, June 10. Rainfall totals varied from 0.4 to 2 inches and foliage was wet all day.

Rain and the possibility of strong storms (hail) are forecast for Wednesday (June12). The upcoming week is forecast to be a little warmer with lows in the mid-50s and highs near 80. We are about a week behind the average of the last five years in terms of growing degree days (GDD). We are behind 2010 and 2012, but very close to 2008, 2009 and 2011. Check your local weather station and conditions at Enviro-weather.

Southwest Michigan GDD summary from March 1 to June 9

Tree fruit

Fruit are sizing well with recent rains and moderate temperatures. Rose chafer beetles showed up over the past week. In recent years, this pest has been generally a minor problem. Oriental fruit moth numbers continue to drop as the first generation flight comes to an end. San Jose scale crawlers should emerge about 780 GDD50 after Jan. 1; currently, the Southwest Michigan Research and Extension Center (SWMREC) is at 618 as of June 10.

Potato leafhoppers have been found and growers should protect vulnerable crop, especially young trees. New plum curculio egglaying damage to fruit should decrease according to the Cornell University model. The rains of June 10 were an infection event for most diseases.

Apricots are about an inch in diameter.

Peaches are about 25 to 30 millimeters in diameter. June drop has reduced the crop. Growers continue to hand-thin where needed. Some varieties in some locations have very high crop loads. The estimated first commercial harvest of Redhaven peach for Berrien County is estimated to be about Aug. 2. This estimate is based on growing degree day accumulation from Jan. 1 to June 3.

Oriental fruit moth trap catches continue to decrease as the first generation is ending. Flagging of branch terminal due to oriental fruit moth larvae should be showing soon. Bacterial spot symptoms have appeared on leaves of susceptible varieties. Developing fruit are susceptible to bacterial spot and rusty spot (powdery mildew) until about pit hardening.

In cherries, exposed fruit is still susceptible to plum curculio egglaying.

Sweet cherries are 15 to 27 millimeters in diameter and early varieties have been coloring. Bird feeding has started. They should be protected against plum curculio and cherry leaf spot. Sweet cherries are always susceptible to brown rot.

Tart cherries are 12 to 13 millimeters with hard pits. Two distinct sizes of fruit are visible with June drop continuing. Crop potential looks good to very good for many farms, but light for some. Areas near Berrien Springs and eastern Van Buren County have a lighter set due to the May 13 freeze. Growers should protect against plum curculio and leaf spot. Leafspot symptoms are easy to find in some orchards.

Plum fruit are 25 millimeters (Shiro) or 20 millimeters (Stanley) in diameter at SWMREC. Plum growers should be protecting against plum curculio and black knot. Black knot controls are needed until active shoot growth slows in early to mid-summer. Bacterial spot symptoms are causing small, water-soaked spots in leaves of some varieties, resulting in shot holes as the spots turn brown and drop out.

Apples are 1 inch in diameter for ‘Golden Delicious’ to 1.5 inches for ‘Zestar’. Natural and chemical-induced fruit drop continues in area orchards. Growers with too much crop potential will need the use of ethrel and, given the mild temperatures forecast for this week, any further chemical thinning is almost impossible (see the Michigan State University Extension article “Apple thinning pointers for 2013”). Hand-thinning apples should start as soon as possible. Growers with a heavy crop will want to use NAA to enhance return bloom.

Red Delicious apples at 1 to 1.25 inches. Photo credit: Mark Longstroth, MSU Extension

Fire blight symptoms showed up on terminals June 3 in Berrien County. Close examination showed evidence of earlier blossom infections, perhaps from the May 9 infection period. Apple scab ascospores trap catch numbers have decreased to low numbers for the June 10 rain. This indicates that primary scab season is nearly over. Scab symptoms from several infection events will appear soon. In orchards with secondary scab lesions on the leaves, growers need to maintain protective sprays to prevent further spread of the disease.

Cedar apple rust symptoms are also appearing. There have also been a lot of inquiries about the orange growths on junipers. Apples are also at risk to plum curculio and tarnished plant bug. Overwintering obliquebanded leafroller larvae have been feeding on shoot tips – trap catch has started to increase, indicating the flight of the spring generation has started. Based on the May 18 biofix, egg hatch for codling moth was expected to begin June 4 using SWMREC’s Enviro-weather station data. Spotted tentiform leafminer mines are apparent.

Pears fruit are approximately 1 inch in diameter. Growers should continue to protect against pear scab and scout for fire blight and pear psylla activity.

Small Fruit

In grapes, ‘Concord’ is about 75 percent full bloom and ‘Niagara’ is about 80 85 percent full bloom at SWMREC and elsewhere. Wine grape varieties are also beginning to bloom. Check progress of the grape berry moth model on Enviro-weather, which predicts grape berry moth development and the start of second, third and fourth generation egglaying (810, 1,620 and 2,430 GDD base 47 F from the biofix of wild grape bloom, respectively). We set biofix for grape berry moth (50 percent bloom on wild grape, Vitis riparia) in some parts of Berrien County on May 25 and other parts of Berrien and Van Buren counties on May 26 to 28.

Grape flea beetle larvae can be found feeding on foliage, but rarely cause significant harm. Now that we have reached bloom, growers should be maintaining thorough coverage of clusters to achieve good disease control. Phomopsis is easy to find on foliage in vineyards that have not been treated. Keep developing fruit protected at least through bunch closure.

The weather is becoming more favorable for black rot infections. More black rot is beginning to appear now on leaves, particularly next to mummified berries that were left on the vines from last year. Black rot infection requires six to seven hours of leaf wetness when temperatures are in the 70 to 80 degree range. Consult the 2013 Michigan Fruit Management Guide (E154) for recommended fungicides.

Downy mildew needs three hours of leaf wetness at 70 F and two to three hours at 80 F. Powdery mildew control should be applied now for problem areas or highly susceptible varieties. Begin checking leaves inside the canopy closest to the trunk for powdery mildew. Powdery mildew is favored by high humidity and temperatures in the 68 to 81 F range.

Blueberries have green fruit and fruit set is generally heavy. Most irrigated fields have very good yields following the 2012 drought. Bloom and fruit set are much lighter in fields that were not irrigated last year. Red leaves from cool weather are fading. Shoots with a heavy fruit load have stopped growing, but young shoots without much fruit are actively growing.

Growers have been applying sprays to control fruitworms and suppress fruit rots such as anthracnose and phomopsis. The Anthracnose Disease Prediction Model Handout posted at the Michigan Blueberry Facts website explains how to use the anthracnose prediction model on Enviro-weather. Note that the output for this model has the earliest rains at the top so the most recent rains are at the bottom of the page. June 10 was an anthracnose infection period. Cherry and cranberry fruitworm egglaying is well underway. The cranberry fruitworm model on Enviro-weather indicates that egglaying is 50 to 75 percent complete.

Strawberry harvest has begun. Tarnished plant bug is active now through harvest, causing deformed fruit and button berries. Evidence of poor pollination can also be found on some strawberries. The misshapen fruit looks similar to damage caused by tarnished plant bug. With tarnished plant bug, seed size is uniform throughout the berry and in sunken areas. With poor pollination, seed size is smaller in sunken areas of the fruit.

Brambles are blooming. Black raspberry bloom is ending. Blackberry and summer raspberry bloom continues. Only fungicides are used during bloom in brambles. Avoid spraying blooming fields during the day to prevent bee injury. Orange rust has been found on summer raspberries. Remove and destroy plants with orange rust. Once visible symptoms appear, it cannot be treated and contributes to a buildup of inoculum in the field. Fungicide applications only reduce the spread of new infections. Fall raspberry shoots are 2 to 3 feet high.

Upcoming meetings

The next Monday fruit IPM meeting is on June 17 at Fruit Acres Farms at 5 p.m. These weekly meetings are good for one RUP credit and will continue through the end of June.

Pre-Harvest Blueberry IPM meetings are scheduled for June 20 in Van Buren County and June 27 in Ottawa County.