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| Vegetable Crop Advisory Team Alert newsletter | |||||||
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| Vol. 23, No. 11, July 9, 2008 |
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| In this issue Vegetable insect update Downy mildew confirmed on the west side of the state Downy mildew confirmed in cucumbers located in Monroe County, Michigan Warm, wet weather favors early appearance of several vegetable diseases Glyphosate injury on tomato Hail damages central Michigan corn and soybean fields Regional reports Weather news |
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| Vegetable insect update
European corn borer and corn earworm The first flight of European corn borer moths is winding down in most areas. The number of moths caught in pheromone traps during the past week (July 1 - 8) has decreased in most locations (see charts below). However, any sweet corn with ears or snap beans or peppers with fruit are still at risk for corn borer infestation. We continue to catch low numbers of corn earworm moths in pheromone traps (less than 1 or two moths per night). Corn earworm, a migratory pest, entered the state much earlier than usual this year and will be here for the rest of the season. Also, we can expect continued earworm migration as the season progresses and any strong weather fronts from the south can bring in large numbers of moths. We are recommending sweet corn growers continue to treat sweet corn with ears and snap beans and peppers with fruit to prevent infestation by European corn borer and corn earworm. Right now we recommend a spray interval of five to six days. When populations of either pest start to increase or temperatures increase, this spray interval will need to be shorter. Bt sweet corn is protected from European corn borer and should be safe from corn earworm given the low number of earworm moths present. Later in the season if corn earworm populations are higher and the silk starts to brown, one or two pyrethroid sprays may be necessary to prevent earworms in the tips of the ears. |
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| Aster leafhoppers Aster leafhopper numbers are moderately high in many celery and carrot fields. The most recent results from tests of leafhopper aster yellows infectivity show fairly high infectivity rates. Almost six percent of leafhoppers collected from a carrot field in Oceana County on July 2 were infected with aster yellows. Infectivity rates of leafhoppers collected from celery fields in Allegan, Ottawa and Newaygo counties from June 26 to July 2 were from seven percent to 10 percent. These are higher infectivity rates than we have experienced this time of year, especially for celery fields in southwest Michigan. We are currently recommending a treatment threshold of six to 10 leafhoppers per 100 sweeps for carrots and three to six for celery. We have still not been able to collect enough leafhoppers from mid- or eastern Michigan to test, but growers should use these same thresholds. Lettuce growers should use a threshold of two to four leafhoppers per 100 sweeps. Remember, it takes several weeks for symptoms of aster yellows to develop in the plant, so insecticide treatment can be discontinued two to three weeks before harvest.
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Downy mildew confirmed on the west side of the state
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| Downy mildew confirmed in cucumbers located in Monroe County, Michigan Mary Hausbeck Plant Pathology Note: This article was originally made available Thursday, July 3 in the web edition of the Vegetable CAT Alert. On July 2, a technician from my lab detected downy mildew on cucumbers growing in Monroe County. This field was selected for scouting because it is where the spore trap is running (see spore counts at end of this article). The infection is very light in this field and no fungicides had been applied. Based on the leaf samples, the infection is relatively recent. What I find to be worrisome is that all five spore traps in the state have now detected low levels of downy mildew spores in the air. With this field occurrence and recent storms, it is guaranteed that the spore counts will increase and outbreaks become more numerous. I find it hard to believe that this outbreak in Monroe County is the only one in the state. Therefore, it is crucial that cucumber growers in the state begin their downy mildew spray program immediately! For the processing pickle growers who may have only recently planted, it is important to remember that young seedlings readily become infected with downy mildew. Seedlings that have their cotyledons infected with downy mildew create a miserable situation and must be avoided. Banded fungicide sprays over very young plantings can save a significant amount of money. Be assured that my program has tested hundreds of fungicide programs. The only fungicides that we can recommend are those listed in the two tables below. However, if the intervals are stretched or the rates lowered, these programs will not protect cucumbers against downy mildew as the disease intensifies in the state. If you are growing other sorts of cucurbits such as pumpkins, zucchinis, gourds, or squash, it is important to note that these crops are not as susceptible to downy mildew as cucumbers. Sprays for these crops can be delayed until downy mildew is noted in that particular county as long as they are being scouted frequently. In past years, melons have become infected with downy mildew and should be treated with a protective fungicide program. For melons, the program can be a bit less intensive than the program recommended for cucumbers. |
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| Warm, wet weather favors early appearance of several vegetable diseases Based on the disease outbreaks that we are seeing, I could swear that it is the middle of August. The wet weather early on in the growing season coupled with some warm nights has set us up for trouble on several fronts. I fully anticipate that this season will be tough on growers who are trying to rein in spots, blights, mildews and rots. Here’s the scorecard: Carrots Cercospora is a fungal pathogen that has been found in two areas of the state. This pathogen causes a blight that affects both old and young foliage. Small, circular lesions occur at first, but expand to affect large portions of the leaves. Cercospora can develop quickly and is often more difficult to control than alternaria blight. When cercospora develops on the petioles of the carrots they become weakened and yield is negatively impacted. Fields with this disease can be treated with fungicides including chlorothalonil (ex. Bravo) and the strobilurins (Quadris, Cabrio, Pristine, or Flint). Remember that the strobilurin products are similar in their activity and should not be overused. A good fungicide program will alternate applications of chlorothalonil with a strobilurin. The TOM-CAST disease forecasting system can be used to time sprays for both Alternaria and Cercospora. Bacterial blight has also been confirmed in a processing carrot field. This particular sample was especially disturbing because of the extensive amount of infection and blighting of the young, expanding leaf tissue. In some instances, bacterial blight on carrot can look dark and almost oily. However, this disease can also appear as a light brown blight that can resemble Alternaria. Bacterial blight can infect young foliage much like Cercospora blight whereas Alternaria blight infects older, senescing leaf tissue. Bacterial blight cannot be managed with those products used to limit Alternaria and Cercospora. Only copper-based products limit bacterial blight. Copper sprays must be applied frequently (minimum every seven days) with thorough coverage of the foliage (no skimping on the amount of water in the spray tank). The TOM-CAST program cannot be used to time sprays for bacterial blight. Copper sprays are limited in what they can offer for bacterial blight of carrot. If the spray interval is stretched beyond the seven days, then the copper applications cannot offer help. The coppers can help limit the spread of the disease and protect the newly emerging foliage. Coppers can reduce the severity of the disease, but they will not cure the blight. Asparagus Rust and purple spot were problems early on this spring, so I don’t expect them to go away this summer. The TOM-CAST system can be used to time fungicide sprays for purple spot on asparagus fern. The primary fungicide that is recommended for use against purple spot is Bravo. Rust is controlled through applications of Folicur that can be alternated with Bravo (chlorothalonil). The TOM-CAST program cannot be used to time fungicide sprays for rust. In cases where disease is not yet established, Mancozeb can be used in place of Bravo to maintain a level of protection. However, if disease is detected, Bravo will be better able to limit both purple spot and rust and will weather better than Mancozeb during wet periods. Asparagus growers should do everything they can do to protect their fern and maintain its vigor into the fall. Green, healthy fern will produce the carbohydrates needed for yields next year. Pumpkins and hard squash Powdery mildew has been found in two locations within the state. Yes, this is a full month earlier than what we would expect. However, it is not the first time that we’ve had powdery mildew occur prior to the Fourth of July. Scouting will be the key in being able to delay powdery mildew fungicide applications. By scouting, I mean walking the field and looking for the white powdery colonies on the lower leaves and the undersides of the leaves. Scouting via a pick-up truck going down the road at 50 mph doesn’t count. Once the very first powdery mildew colonies are observed, a spray program should begin immediately. Growers differ in the types of products that provide a good level of control. While some growers are satisfied with Nova and the strobilurins (Cabrio, Flint, Quadris, and Pristine), others note that a combination of Bravo + Topsin works well. Part of the reason why the reports vary so much is that some of our powdery mildew isolates may have developed resistance to one or more of our commonly used fungicides. The key to a successful powdery mildew program is to monitor the level of disease in your field carefully to determine whether your fungicide program is working and if it isn’t, change the products you’re using. Peppers Phytophthora crown rot is affecting some pepper fields in the state. We have two field plots testing a commercially resistant cultivar against a susceptible cultivar. Both the resistant and susceptible cultivars are being sprayed with several different fungicide programs. This research is being conducted in my program by Jennifer Foster, a Master’s student from Ontario. At this point in time, all fungicide programs are struggling to protect the susceptible ‘Red Knight’ peppers even though we are using raised plant beds. We chose ‘Paladin’ as our resistant variety to screen in the field since it held up better than ‘Aristotle’ in our greenhouse experiments. At this juncture, the ‘Paladin’ peppers are surviving irrespective of the fungicide program used. I expect that may change as the trial continues. I’ll provide updates as the season progresses. Registered fungicides for use against Phytophthora in peppers include Tanos, Ridomil Gold Copper, Phostrol (or Fosphite, Prophyt), and Acrobat (Forum). Remember, all sprays should be targeted to the base of the plant to protect the lower stem and crown portion. |
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| Glyphosate injury on tomato Several tomato samples have been submitted to the lab over the past ten days with symptoms consistent with glyphosate injury. In most of these cases, the injury resulted from glyphosate spray drift likely from neighboring corn and soybean fields. Occasionally, the injury resulted from glyphosate contamination in the tank used to apply pesticides to the tomatoes. Specific symptoms of glyphosate injury will vary depending on several factors including exposure dose, tomato growth stage and growing conditions after exposure. Glyphosate is translocated inside the plant to the newest meristematic regions; therefore the newest growth will be most injured. Tomatoes injured with glyphosate will have distorted new growth with cupped, fringed and small leaflets. Often, the newest leaves will contain a proliferation of buds and small leaflets. Many of the leaflet bases will contain a yellow to white discoloration –a diagnostic clue of glyphosate injury on tomato.
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| 1 - SW Michigan Research and Extension Center Ron Goldy Weather Temperatures were near normal for the period with lows from 48°F to 69°F and highs from 71°F to 86°F. There was one to four inches of rain across the immediate area. Crop report Watermelon and cantaloupe have softball-sized or larger fruit. Cucumber, yellow squash and zucchini harvest continues with volume increasing as direct seeded fields come into production. Pumpkins and fall squash are blooming and runnering. Growers need to be aware of squash vine borer activity at this time and protect susceptible plants. Powdery mildew has been found on squash and pumpkins. Pepper, eggplant and tomatoes are growing well with increased temperatures. Tomato harvest from tunneled fields will begin soon. Colorado potato beetles have increased in eggplant fields. Sweet corn harvest from row covered plantings began over the weekend. Some smut and Stewart’s wilt is present in some fields. Green bean harvest has begun. Tarnished plant bug populations have greatly increased and need to be controlled in susceptible crops. An increase in mite populations has also been noticed. |
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| 2 – Grand Rapids Area
Weather West-Central Michigan's weather continues to be too wet. Southern Kent and northern Allegan counties have seen as much as four to five inches since last Wednesday, July 2. A few of the muck vegetable producers who sustained the most crop damage from the early-June storms were set back once again. Upland fields are wet as well. Soybeans appear to serve as a good indicator of how the saturated soils are stressing crops. Many of these fields exhibit uneven growth, displaying various shades of yellowish-green. Crop report On muck soils, crop progress depends on the degree of rainfall and how well water is carried away from the field. In much of southern Kent and northern Allegan Counties, the fields remain very wet. Some of the celery, onion, leek, sweet corn and cabbage growing in this area has been destroyed or stressed. Some growers anticipate small onions because sufficient leaf area has not developed. Transplanting and other field activities have slowed or stopped altogether. Some growers are hiring aerial applicators to continue pest control operations. Vegetables growing on muck farther north, south and east of this area are faring somewhat better, with development proceeding at a more normal pace. The second radish crop appears to be doing well. On upland soils most crops are doing fairly well, although I will soon investigate reported hail damage in central Ottawa County. Hopefully, the damage will be fairly isolated. Throughout the area, sweet corn growth ranges from the two-leaf to late-silk stage. Cabbage is being harvested while new transplants begin growth. Vine crops and upland cabbage looks good. Tomatoes and peppers look good overall and are developing fruit. |
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| 3 – Oceana County
Weather Oceana County has had several good rains over the last two weeks. Unfortunately a little hail has accompanied the rain in some of the fruit growing areas. Warmer temperatures have also added plant growth on a number of plots. Crop report The last producing asparagus fields were shut down around July 3, making 2008 one of the latest harvest seasons in recent memory. While official numbers haven’t been published yet, the total crop produced a few million pounds more than last year, but still fell short of the state’s five-year averages. Wet weather has increased the threat of foliar diseases, especially in young fields where fern is well established. Mary Hausbeck’s lab identified bacterial blight in Oceana County carrots, and area scouts report the presence of both fungal blights, although this has not been confirmed by lab results. All of my carrot Tom-Cast sensors are set and we have run up quite a few Disease Severity Values during the last ten days of warm, wet weather. Zucchini, pumpkins and pickles are emerging normally and growers are sending hoeing crews through to control weeds flushed by the heavy rains. The early July snap bean plantings have mostly emerged and stands look good so far. In sweet corn, warmer weather has improved growth in July, but the crop is still way behind normal. |
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| 4 – Mason-Newaygo counties
Weather Temperatures have been seasonal during the past two weeks. Rainfall amounts in the area have been variable but the end results have been about the same. At the Fremont Enviro-weather station, 1.86 inches has been reported in the past two weeks, with 1.46 of this total received on July 2. Growers near the Fremont station reported up to 2.8 inches on July 2, while in the Grant area about 1.25 inch was received. In Mason County amounts were less on July 2 with only 0.56 inch at the Ludington station, but 1.01 inch was received on July 7 for a total of 2.03 inches during the past two-week period. Crop report Growth of carrots has progressed nicely the past two weeks. Fields of dicer type processing varieties are now developing rots at 0.50 to 0.75-inch diameter. As reported earlier there are some thin stands in some fields and more notably on the fields where soils are lighter and sandier. Onions have not started to bulb yet, but fields look good with growth at the six leaf stage and 15 to 18 inches in length. Spinach harvest was completed on July 3. Harvest of turnips and beets is underway in Newaygo County with the potential for good crops reported. Fields of winter squash are now growing well and beginning to run with plants 18 to 24 inches in length. Cucurbit crop growers in the area have been alerted regarding control measures for downy mildew. Snap bean growth at the Mason County European corn borer site is now at the first trifoliate stage. European corn borer trap counts on July 8 were 1 - 0 - 2. Corn earworm trap catch at the Mason County sweet corn site on July 8 found seven in the large trap and two in the small trap. The fields are growing well with the first tassel just forming. Maturity is about a week behind normal. The two moths that I reported as western bean cutworm in my June 25 report were not western bean cutworm, therefore no western bean cutworm has been caught to date at the Mason County site. The sample sent to MSU for confirmation was identified as winter cutworm, noctua pronuba. |
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| 6 - Monroe County
Weather We have received plenty of rain in the past two weeks. There are some wet pockets in most fields with dying plants. According to the Enviro-weather station in Dundee we received a total rainfall of 4.18 inches during the past two weeks. I have heard from several growers that received from 1 to 4.5 inches of rain. Soil temperatures this last week ranged from 44°F - 88°F. Crop report Sweet corn is making very good growth. Harvest has begun in some early planted under tunnels fields. In general, most of the fields are in silking stage. Many growers expect to begin harvest next week. Peppers are looking good. Most plants are setting very good fruit. Some farmers have started to harvest. There is some water injury to peppers in the low lying areas of many fields. Cucumber fields are developing well although cucumber downy mildew was identified last Wednesday in one local field. Since we are in a period of high precipitation, a weather pattern which is very conducive for spore development, growers need to pay a close attention to restrict further spread of the disease. Cucumber beetles are present in many cucumber fields. Pumpkins, melons and squashes are improving. Pumpkins have flowers in many fields. Market tomatoes are just starting to be harvested and have very nice fruit quality. There is good fruit load in many early planted market and processing tomato fields. There are not any severe insects or diseases present at this time. I saw two processing tomato fields with herbicide drift appeared to have come from adjacent glyphosate resistant corn fields. Potatoes are in a variety of growth stages from maturing vines to tuber settings. I have seen some early symptoms of rhizoctonia (Photo 1) on some table stock varieties. Colorado potato beetle (Photo 2) activities have been found in several fields. Most of them are in high numbers and growers are following spray schedules.
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| Weather news Clear skies and less humid conditions prevail after the passing of the cold front on Tuesday, July 8. With higher pressure moving into the region, clear or partly cloudy skies will be the norm for our state. A warm front looks as though it will be passing through the region on Friday, producing rainfall across the central part of the Lower Peninsula to the Upper Peninsula. Temperatures during the next few days will be lower because of the cold front that passed through our region, with highs Wednesday generally ranging from the mid-60s in the north to the low 80s south and lows Wednesday night and Thursday morning from the mid-40s north to the low 60s south. Temperatures will be variable from day to day across the state until Sunday when they become steady after the passage of the frontal system. On Thursday, highs will be in the low 70s in the north to low 80s in the south. Friday will see highs in the upper 70s to upper 80s with some thunderstorms. For the weekend, temperatures will be in the upper 70s in the north to upper 80s in the south. The National Weather Service 6‑10 day outlook covering July 14 through July 18 calls for normal temperatures and precipitation across the state. The outlook for the 8-14 day period (July 16 - 22) calls for above normal temperatures and near normal precipitation. The long term outlook shows that conditions for the rest of the month should be near normal, with a gradual shift back to a more seasonable range in conditions. |
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