July 30, 2008
In this issue
§ Vegetable insect update
§ Onion disease alert
§ Regional reports
§ Weather news
Next issue August 6
Beth Bishop
Entomology
Numbers of European corn borer moths captured in pheromone traps from July 22 to 29 have increased slightly, as the second flight has begun. No significant migration of corn earworm into the state has occurred during the past month and trap counts are low.
Squash bug adults, nymphs and eggs have been observed in cucurbit plantings. Now is the time to control them. If you wait until the nymphs grow large and the row fills in, they are extremely difficult to control.
Squash bugs are primarily pests of squash and pumpkins, but can sometimes occur on melons. Squash bugs suck juices from the plants and may cause leaves to die and vines to wilt. Later in the season squash bugs feed on fruit, causing collapse.
Adults are three-quarters of an inch long and dark grayish brown with wings held flat over the abdomen. Eggs are laid in clusters on the underside of leaves and are orange when laid, but soon turn metallic bronze. Young nymphs are pale-green to white and older nymphs are grayish-white. Nymphs are wingless.
Small nymphs feed in groups on the underside of leaves. Larger nymphs feed individually and both large nymphs and adults are very mobile. Insecticides applications must target the small nymphs. An insecticide application is warranted when one or more eggs masses per plant are present. Consult bulletin E312: 2008 Insect, Disease, and Nematode Control for Commercial Vegetables for insecticides registered to control squash bugs on your crop.
Mary Hausbeck
Plant Pathology
Downy mildew was verified by my lab yesterday afternoon from a field in the mid-Michigan area. This disease is not unexpected given the rains and cooler, moist weather that we’ve experienced this year. Unfortunately, downy mildew is an especially devastating disease because it spreads rapidly and is not readily controlled. Downy mildew of onion is caused by the pathogen, Peronospora destructor, and first infects older leaves, occurring as pale, elongated patches that may have a grayish-violet fuzzy growth. Symptoms of the disease are best recognized when dew is present in the morning. Infected leaves become pale green, then yellow and can fold over and collapse. Premature death of onion leaves reduces bulb size. The downy mildew pathogen initiates infection during cool temperatures (less than 72°F) and wet conditions. Multiple infection cycles can occur in a season. Spores are produced at night and are easily blown long distances in moist air. They can germinate on onion tissue in one and a half to seven hours when temperatures are 50°F to 54°F. High daytime temperatures and short or interrupted periods of humidity at night can prevent sporulation. Overwintering spores, called oospores, can form in dying plant tissue and can be found in volunteer onions, onion cull piles, and in stored infected bulbs. Oospores have thick walls and a built-in food supply so they can withstand unfavorable winter temperatures and survive in the soil for up to five years.
Research studies have shown that weekly applications of
mancozeb (available as Dithane, Manzate, or Penncozeb) protect against downy
mildew when spray coverage is good and sprays are begun before disease appears.
Some growers choose to include Ridomil Gold MZ in alternation with mancozeb
although this program is more costly. We have tested Pristine 38WG in rotation
with Ridomil Gold MZ for downy mildew control. The program with Pristine and
Ridomil Gold MZ in alternation was effective for downy mildew, but is very
costly. It is likely that Pristine alternated with mancozeb would also be
effective, but needs to be tested. In addition to downy mildew, Pristine 38WG
has activity against the leaf blights including purple blotch, Stemphylium, and
Botrytis. In a field test for purple blotch and Stemphylium leaf blight,
Pristine alternated with Bravo Weather Stik was a stand-out treatment. Newer
products for downy mildew control include Acrobat and Reason. While I do not
have
Many
Stemphylium leaf blight is an occasional foliar problem in
The following products are recommended for purple blotch: Pristine, a strobilurin (Quadris or Cabrio), and Rovral tank-mixed with Bravo.
Botrytis has been detected this year in onions. It is caused by a fungus (Botrytis squamosa) that survives in onion trash or in soil by means of sclerotia (hard, black survival structures) which germinate in the spring, forming ascospores that begin the disease cycle.
Germinating sclerotia are small and very difficult to find, but they have been reported onion leaf trash. Once the initial infections occur, spread is controlled by weather conditions. This fungus forms its conidia (the spore stage that spreads the disease) only on dead or dying tissue, and only after 60 to 72 hours of continuous high humidities (75 to 100 percent) at temperatures averaging between 54°F and 75°F.
Conidia formed under these conditions are spread by wind currents, land on healthy tissue, and infect after a minimum of six hours of leaf wetness. The longer the leaves remain wet, the more infection that occurs. The fungus forms rather small, white lesions about the size of a pinhead surrounded by a light green halo. Most of these lesions do not enlarge, but a small proportion will enlarge, girdle the leaf, and cause blighting.
The higher the humidity and the longer the periods last, the more leaf blighting that will occur. Bravo has always been excellent for leaf blight control, but mancozeb and Rovral also give good control. In previous years, tank mixes of Rovral with either mancozeb or Bravo have been especially effective where botrytis leaf blight and purple blotch are both present. Pristine will also do a good job when both botrytis leaf blight and purple blotch are a problem.
Bacterial diseases are showing in many onion fields, especially those that experienced heavy rains earlier this summer. It is likely that naturally-occurring soil bacteria were washed into the bulb and leaf whorls where they have multiplied and now causing a rot. It will be difficult, if not impossible, to reach those inner onion tissues that are infected with the bacteria. The only product that is proven and recommended for bacterial diseases is copper. I’ve heard a lot of talk about spraying bleach and I do not recommend that growers do that. Bleach will become inactivated as soon as it comes in contact with leaf tissue or soil. It has no residual and will not protect the leaf tissue. Copper is a proven bactericide with a residual action which is a fact that is supported by years of studies on onions and other crops that are affected by bacteria. To lessen the concerns of phytotoxicity on onion leaf tissue, spray copper at a time of day when the solution can dry readily. The longer that copper stays in solution, the more likely that it may cause some plant tissue burning. When using copper sprays to combat bacterial disease, the spray interval should be at least every seven days.
Ron Goldy
Temperatures have been near normal for the period with lows from 54°F to 64°F and highs from 74°F to 88°F. There was only 0.10-inches of rain across the area for the week.
Sweet corn harvest has been slow due to cool temperatures, but volume has finally increased with large commercial fields being harvested this week Growers should be concerned about second generation European corn borer and corn earworm.
Tomato harvest continues with volume increasing as more fields come into production. Hornworm and fruitworms can be found in some fields.
Phytophthora symptoms continue to show up in pumpkin, fall squash and other susceptible crops. Otherwise plants are growing and flowering well.
Early cucumber, zucchini, and yellow squash fields are finished and being removed with some being replanted. Early virus symptoms are showing up.
Pepper and eggplant harvest has begun.
Tarnished plant bug populations have decreased.
There will be an open house for the high tunnel system on July 31 from 7:00 PM to 9:00 PM at SWMREC.
Bill Steenwyk
Last night and this morning (Wednesday, July 30), the area
near my home in
Crop report
Crop growth and harvest results have been variable. Celery harvest for fresh and processing markets continues. Reports range from good, to fair, to none for those who lost their early crop to flooding. Diseases such as fusarium wilt and aster yellows are present. Some fields are not sizing out as well as hoped for. The pale cast suggests nitrogen deficiency.
Onions are sizing
out considerably. Bacterial and fungal diseases are reported in a number of
fields. The bacterial rots usually appear on plants with physical injury or
those that have been attacked first by fungi. This year, however, it may be
that the many fields in
Sweet corn harvest has been underway for over a week and reports are mixed. Fields that shed the heavy June and early July rains appear to be yielding quite well, while those that were floodwater-stressed are less productive with poorer tip-fill. A degree of nitrogen deficiency is also evident in the latter. Common rust is present at all growth stages in some fields. Some wormy ears are present, but not a major problem. Growers are dealing with the usual challenge of bird control. Corn borer and corn earworm moth counts remain very low.
Vine crops are doing well, but some powdery mildew, downy mildew and phytopthora is present. Tomatoes and peppers appear to be progressing quite well. The same is true for cabbage where harvest continues.
Some fields are quite weedy. It is evident that the earlier excessive rainfall has diminished herbicide performance and limited the opportunities to come back in with timely post-emergent sprays.
Norm Myers
Weather has continued to be dry this last week, with both Hart and the Asparagus Research Farm reporting no rainfall. Irrigation is underway where it is available.
In asparagus, heavy dews and warm weather have kept the disease pressure high in spite of the lack of rain. My TOM-Cast sensors have put on seven or eight Disease Severity Values over the last week.
The results of the early, high aster yellows infectivity rate are now pretty evident in carrot fields. Irrigation is being used where ever it is available.
We continue to find a little more virus in our processing zucchini each week and powdery mildew pressure has been very steady. Cucumber beetle continues to be a problem, and I have had my first report of squash bugs being active.
Irrigation is also being used on snap beans wherever it is available.
In sweet corn, the European corn borer traps continue to be low. I haven’t caught any corn earworms for the second week in a row.
Jim Breinling
The dry weather pattern persists in the area. Even though
fronts have moved through the area there has been no rainfall reported at both
the Fremont
and Ludington
Enviro-weather
stations. Rainfall amounts that have occurred in the area have been reported to
be about 0.25-inch. High temperatures at
The carrot crop situation continues much as the previous week with leafhopper activity and increased leaf blight pressure. Irrigation systems have been going steadily in carrot fields during the past week.
Snap bean fields
are growing well with most fields being irrigated. European corn borer counts
at the
The corn earworm trap counts at the sweet corn site in
Fruit set has begun in fields of butternut squash for processing. Irrigation of this crop has also been steady during the past week.
Hannah Stevens
It has been a relatively cool and dry week in most locations
and irrigation was underway for the first time in a while. A thunderstorm this
morning (July 30) in northern
The carrot crop on the muck soils is being shipped and favorable growing conditions have resulted in a good crop so far. Onions are sizing well although thrips are continuing to be challenging, as well as foliar diseases such as purple blotch and Botrytis. I have seen some enormous sweet onions fresh peeled for retail sales.
Sweet corn is finally on the market. An occasional corn borer tunnel can be found in the ear. The appearance of common rust is causing some concern and I expect some acres have been treated. Vertebrate pests including raccoons and blackbirds are causing enormous losses in both early and late corn, and are in such high numbers they are difficult to control. One grower reported raccoons devastating the tiny unfilled ears of late corn.
Downy mildew has been identified on slicing cucumber in
The tomato harvest is beginning. Fungal diseases need very close attention as vines are vigorous and the fruit load is heavy. For disease that does not seem to be controlled, bacterial disease such as speck and canker may be the culprits. The blowing soil that happened on a number of days this spring allowed speck to gain entry into leaves and fruit and the tiny specks may be found on fruit. Cool weather at flowering caused catfacing on the first fruit.
Japanese beetles have emerged in huge numbers this past week. While they are generally regarded to be a concern in home landscapes, they have a very large host range and can be found on many plants, including weeds and crops.
Growers and others are invited to join me and two MSU
vegetable crop specialists at the All Vegetable Crops Twilight Meeting on
Thursday, August 7 at UAP,
Dinner is at 6:30 PM and is courtesy of UAP. At 7:00 PM our program will feature Beth Bishop who will discuss some current insect pests affecting vegetable crops and what research she is engaged in. Mary Hausbeck will help us understand some of the disease problems of concern at the present time and what control strategies her research suggests.
New publications and upcoming programs will be introduced. Growers are encouraged to bring problem weeds and other samples in plastic bags for discussion before the meeting.
Please contact Hannah Stevens at 586-469-6440 or at stevensh@msu.edu by Monday, August 4 if you plan to attend so that we will have dinner and materials for you.
Sudeep Mathew
Last week’s dry weather continued all week long. Every one is looking forward to a rain. Most of the growers irrigated this past week especially for maturing potatoes. Soil temperatures ranged from 66°F – 83°F. According to the Enviro-weather station in Dundee, the total estimated evapotranspiration rate for this past week was 1.39 inches.
Harvest of sweet corn that was planted early under tunnels is over. Other fields’ sweet corn ranges from different growth stages to harvesting. There is European corn borer damage in some fields. I could see nitrogen deficiency in sweet corn on sandy soils. It could be the impact of early July rain, followed by the dry weather which has caused substantial leaching and denitrification on sandy soils. There is some uneven corn growth and development due to dry soil conditions. I haven’t found any European corn borer or corn earworm in traps.
Cucumber, squash, zucchini and melon harvest is taking place. The downy mildew situation is stable. Vine crops are showing stress from the dry weather with smaller fruit sizes. Melons have good fruit sizes and quality. Squash bug eggs and nymphs (Photo 1 and 2) were found on zucchini plants. Powdery mildew was found in butternut squash, yellow squash and pumpkin (Photo 3). There was one squash vine borer found in the trap.
Peppers are of good quality. Fresh market peppers continue to be harvested and marketed this week. Colorado potato beetle was found in moderate numbers in eggplants. Eggplant fruit was also injured by the Colorado potato beetle.
Cabbage pythium stem rot was found on a cabbage field.
Tomatoes continue to blossom and set fruits. Fruit loads are heavy. Heirloom tomatoes are still growing taller. There has been very low disease pressure from fungal pathogens, but bacterial diseases are present in a few plants.
Potatoes have started to mature. Few vines are senescing and most vines are remaining green. Harvest of early planted potatoes started this past week. Fields are getting an average yield of 400 - 450 cwt/acre at this point. Tubers sizes are in the range of eight to 11 inches in circumference (Photo 4). Ten variegated cutworms were found in the trap.
Jeff
Andresen
Agricultural Meteorology
Geography
For the last several days, a broad upper air ridge has
persisted across much of the central
High temperatures should increase from the low and mid-70s far north to the mid-80s south Thursday to the 80s north to low or mid-90s south Saturday and Sunday. Low temperatures are expected to warm from the 50s to low 60s in most locations Thursday morning to the 60s statewide by Saturday. A weather system approaching from the west will bring the next chance for significant rainfall by next Tuesday or Wednesday.
In the medium range period, forecast guidance suggests a
gradual flattening out of the upper air pattern across