| A first report of downy mildew on cucumbers in Michigan
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On August 5, downy mildew was confirmed on cucumbers in This downy mildew is not the same as the commonly occurring powdery mildew. Downy mildew causes symptoms on the leaves similar to a mosaic or angular leaf spot (see images). However, the downy mildew pathogen forms a grayish/purplish fuzz on the undersides of the foliage. This fuzz may be most evident in the morning. The symptoms of powdery mildew include a white, powdery, talcum-like appearance on either side of the leaf, petiole or vine. Downy mildew is an extremely explosive pathogen when the environment is favorable. The fungus prefers temperatures in the 50° to 80°F range. The optimum temperatures are 61° to 72°F. Hot temperatures such as we’ve had in the recent days will not kill this pathogen. A film of moisture from dew or irrigation is needed for the downy mildew to infect the crop. The predicted cool temperatures and increased moisture in many areas will allow the downy mildew to reproduce rapidly and spread widely. Control measures must be taken immediately by all growers in the state to limit this downy mildew outbreak. Some cultivars are more susceptible than others. Some crops are more sensitive to particular strains of the downy mildew pathogen. At this juncture, we must assume that all cucurbit crops in Fungicide sprays must be applied preventively before the pathogen causes disease and reapplied every seven days to ensure protection. Once the pathogen has infected a crop and symptoms occur, fungicide applications are not very helpful. To complicate matters, this downy mildew pathogen is likely to mutate and become resistant to some of the fungicides including the Ridomil-based fungicides and the strobilurins (Amistar, Cabrio, Growers who have used any strobilurin (Amistar, Cabrio, Since the southern states are reporting success with the newer downy mildew fungicides (Tanos, Previcur Flex, Gavel, Curzate, Acrobat), I would prefer that growers use these fungicides rather than relying primarily on the Ridomil-based products. An important problem with the Ridomil fungicides is that the downy mildew can develop resistance to these products. Please note that some of the downy mildew fungicides allow applications to some cucurbit crops but not others. Read and follow the fungicide label! Pre-harvest intervals of the fungicides need to be considered for those crops currently being picked. Curzate and Tanos each have a 3-day PHI. Previcur Flex has a 2-day PHI. Acrobat has a 0-day PHI. Gavel and any Ridomil-based fungicides have a 5-day PHI. Diagnosis in the laboratory of downy mildew takes less than 30 minutes. It is important that any potential downy mildew cases be reported to me and confirmed. My contact information is (517) 355-4534 or e-mail at: hausbec1@msu.edu |
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| Spider mites in vegetable crops | Growers and scouts should watch for spider mites in vegetable crops, including celery, tomatoes and watermelon. Mite populations are responding to hot, dry weather and reduced plant vigor. Most insecticides will not control mites. Agri-Mek is one of the few products with mite activity. Spray coverage needs to be as complete as possible, especially covering undersides of leaves. Check bulletin E-312 for products registered on specific crops. |
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| Vegetable leafminers in celery | Vegetable leafminers are reported from celery. These are highly resistant to most insecticides and treatment with standard insecticides (pyrethroids or organophosphates) will kill natural enemies but not control leafminers, resulting in an increase of problems. Agri-Mek, Trigard and SpinTor are registered and effective for leafminers in celery. Check bulletin E-312 for products registered on specific crops. |
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| Onion thrips in high numbers | Onion thrips numbers are very high in onions, and problems have been reported from tomatoes, also. Thrips in |
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| European corn borer and corn earworm update | The second flight of European corn borers has begun in the southern Sweet corn at tassel and beyond, as well as peppers or snap beans with fruit, are at risk for corn borer infestation. Eggs are laid on the plant surface. After hatching, the small caterpillar feeds on the plant surface a few days before burrowing into the stem or fruit, where it is protected from most insecticides. To adequately control corn borers, a lethal dose of insecticide must be on the plant immediately after the caterpillar hatches. Therefore, for vulnerable crops, a regular spray program is necessary during the second flight of moths. A few corn earworm moths were caught last week in pheromone traps in |
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Regional reports 3 – Oceana County |
Weather We had a little light rain this morning, but the northern portions of the county do not need rain since they have had five to six inches in August. There is a very dry strip along Commodity reports Both major blights are present in carrots but under control. Some aster yellows are showing up but much less than the last two years. Yield potential still looks large in most fields, but some carrots have drowned out in poorly drained fields. In winter squash and pumpkins there has been no sign of downy mildew yet, but plenty of virus signs are present. Set is thin in a lot of fields because of a lack of female blossoms. What pumpkins we have will ripen early, and growers are already worrying about keeping them in good condition until shipping begins in late September. Virus is becoming a real problem especially on yellow varieties of zucchini, where symptoms are more obvious. Phytophthora is also hurting many fields. The feeling here is that processors will come up short this year. Yields have also been erratic due to lack of female blossoms. In snap beans, growers are worried about blossom abortion dropping yields in the earlier plantings. European corn borer moth catches are still low, but I did catch a suspicious moth in my corn earworm trap. |
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| 4 – Mason-Newaygo counties | Weather General and heavy rainfall occurred in Commodity reports There have been some reported symptoms of viruses showing up in some snap bean fields. Numerous spots in fields have been lost due to standing water. There are no European corn borer counts this week due to disruption of traps caused by storm. We have had some feeding and holes in leaves in some fields, which were thought to be result of Japanese beetles. Viruses in vine crops are becoming more severe. Summer squash and pumpkins are affected the most at this time, with winter squash showing few symptoms yet. There were no corn earworm moths found at the sweet corn trap site this past week. |
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| 6 – Macomb, Lapeer, St. Clair counties | Weather Yesterday’s high in the low 90s is becoming typical for one of the hottest summers in memory. Hand pickers are in the fields at dawn and in the evenings to avoid the worst of it, both for comfort and harvest quality. The soil is dry in most areas but as most vegetable crops are now being harvested, moisture is not as critical. Rainfall has been variable, and I have recorded 11.84 inches to date in Commodity reports In sweet corn, European corn borer trap counts remain low, but I discovered 5 to 10 percent infestation of small corn borer larvae in the ears of an unsprayed block of corn, so second generation egg laying is well underway. Bird damage has been an issue for several weeks. Sap beetles follow both worm and bird damage – they are not a primary pest. Growers are anxious about common rust at this time, but I have not seen the cinnamon brown pustules on upper and lower leaf surfaces yet and don’t think fungicides are warranted unless scouting reveals them. In tomatoes, Septoria and Alternaria leaf spot is common in gardens and unsprayed plants at this time. I understand that fruit quality and yields are excellent The pumpkin story is not good at his time although the final outcome is uncertain. Many growers noticed an abundance of male blossoms, yellow foliage, virus symptomsand general decline of fields last week in pumpkins and winter squash. Cucumber mosaic virus was confirmed in two fields. Some fields remain relatively healthy, which might be related to variety, plant vigor or location of the field relative to soybeans. Most growers report seeing no aphids in the virus-infested fields, but striped cucumber beetles may also vector this virus at very low rates. As virus transmission requires few insects, it is not practical to control the virus by eliminating the insects. On the good side, muskmelon and watermelon yields are high and quality is excellent. Yield and quality in carrots is as high as it has been in many years. Bacterial spot has been reported in field of peppers. The presence of corn borers indicates the need to protect the fruit at this time. A Sweet Corn Variety Trial Open House and Program has been scheduled for Wednesday, August 17, The farm is north of Romeo between Powell and M-53. The farm is just west of the Romeo District Court office. Look for the MSUE Extension sign on |
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| 7 - Monroe County | Weather Hot and dry has been the story for our area this last week. Lack of rainfall has forced irrigation systems back into operation. Warm nights at 70 degrees and above has made the harvesting and packing of quality produce more difficult since growers do not have the advantage of cool morning temperature in the products. Commodities reports Sweet corn is in abundant supply and great quality. Second generation corn borers have not been a serious threat with moth catches this week again very low. Egg masses in fields are very difficult to find. Heat has increased maturity rate to a point some growers may end the season at least two weeks earlier than they had planned at planting time. Cole crops are all suffering in the heat. Several growers are continuing to plant for late fall in fields where irrigation is available. Melon harvest continues with great quality melons available. Yields have been tremendous. Flavor has been great with all the sunshine. Pepper harvest is well underway with very good quality. Plants appear to be loaded with fruits for a good continual harvest. Aphids have been difficult for some growers to control this season. Potato harvest continues to move at a slow pace with current high temperatures making it difficult to pack a quality product as tubers come out of the soil early in the day with a pulp temperature above 75 degrees. Leafhoppers have decreased significantly from earlier in the season. Processing tomato harvest has begun this week on a limited basis with many fields now receiving Ethrel applications and harvest to begin on a full scale next week. Market tomatoes are in large supply with very good quality. Size of tomatoes has been very good from the beginning of the packing season. Pumpkins are sizing fruits now with both virus and powdery mildew present in a number of fields. In most fields virus is not serious, but in several fields virus has become a major problem and a concern for potential fruit quality. |
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| Weather changes on the way | After several weeks of a persistent ridging pattern across the central United States, the jet stream will be moving southward during the next couple of days, resulting in cooler and wetter weather for much of the Great Lakes region. A cool front is forecast to move across Temperatures during the next few days will gradually fall back to near or slightly below normal levels with highs ranging from the low and mid-70s north to mid-80s south and lows from the low 50s north to low 60s south. In the medium-range time frame, computer model guidance is suggesting that the core of the jet stream, normally near its northward-most range across central Canada at this time of the year, will at lest temporarily shift southward to the United States/Canada border area. This would result in a fast-moving, west-to-east jet stream flow over Michigan with more frequent incursions of cooler, Canadian-origin air masses (i.e. more cool frontal passages), and more frequent chances for precipitation. The NOAA CPC 6-10 day outlook, covering August 15-19, calls for temperatures to range from near normal in extreme southern sections of the state to below normal elsewhere and for above normal precipitation statewide. The outlooks then suggest that the jet stream will slowly drift back to the north and east, resulting in an 8-14 day outlook (covering August 17-23), which calls for near normal temperatures and below normal precipitation totals statewide. |