August 15, 2007
In this issue
§ European corn borer/corn earworm update
§ Aster leafhoppers and aster yellows
§ Phytophthora and fumigation
§ Powdery and downy mildew in cucurbits
§ Regional reports
§ Weather
Next issue August 29
Beth Bishop
Entomology
During the past week, increased numbers of both European
corn borer moths and corn earworm moths have been caught in most pheromone
traps in southern and central
Recent weather conditions have been favorable for insect migration and corn earworm moth numbers have increased (see http://www.pestwatch.psu.edu/sweetcorn/tool/tool.html). Corn earworm moth populations are still much lower than they were this time last year. Given the current numbers, most insecticides applied to prevent European corn borer damage will also be effective against corn earworm. In corn, earworm moths are attracted to and lay eggs on green silks and insecticides must thoroughly cover the silks to prevent earworms from entering the ear. At these population levels and current temperatures (highs in the mid-70’s to low 80’s), a four to five day spray interval is sufficient to protect against corn earworm and European corn borer.
See Bulletin E-312, 2007 Insect, disease and nematode control for commercial vegetables for insecticide options for control of European corn borer and corn earworm. You can find this bulletin online at http://web4.msue.msu.edu/veginfo/E312. Acephate, a systemic insecticide, is registered on snap beans and peppers (NOT sweet corn). This is the only insecticide that is effective once worms enter the fruit. However, only two applications per year per crop are allowed. Also the pre-harvest interval is seven days in peppers and 14 days in beans, so this is not an effective option close to harvest.
Beth Bishop
Entomology
Aster yellows continues to be rare in southwestern
Aster leafhoppers collected last week from carrot fields in
west central
Mary Hausbeck
Plant Pathology
Phytophthora capsici can survive in the soil for up to ten years, and has the ability to destroy entire crops within days. The pathogen affects the root, stem, and fruit of eggplants, tomatoes, peppers, snap beans, squash, melons, pumpkins and cucumber. Fumigants, combined with good management practices can reduce the likelihood of infection occurring in the field.
Plant pathologists at
The studies were conducted on tomatoes, eggplants, peppers, zucchinis, winter squash, melons and watermelons. Both years the treatments were conducted on grower cooperator farms in fields with severe Phytophthora disease pressure. Treatments of methyl bromide/chloropicrin, chloropicrin alone (100%), and Telone C-35™ (1, 3dichloropropene /chloropicrin) were applied using standard gas-injection knives 10-12 inches below the soil and covered with plastic mulch. Applications of Vapam™ (metam sodium) and K-Pam™ (metam potassium) were made via drip tapes installed under the plastic mulch.
In 2003, each product was applied alone at the higher rates used by growers. For 2004, K-Pam™ was tested alone and in combination with chloropicrin at both the higher and lower labeled rates. Each crop was planted after the appropriate period of off-gassing had expired for each treatment.
Combining the percentage of plants killed by Phytophthora for all crops resulted in significant disease control for all treatments applied in 2003. In 2004, both rates of K-Pam™ applied alone or in combination with chloropicrin were very effective in limiting Phytophthora in all crops.
Applications of methyl bromide/ chloropicrin and chloropicrin alone were also significantly better than the untreated control. The treatment of Telone C-35™ was not as effective in 2004 as it was in the 2003 study.
Data from the 2004 trial shows that applications of both rates of K-Pam™ applied either alone or in combination with chloropicrin were very effective in controlling Phytophthora in both the melon and watermelon plantings. Applications of methyl bromide/ chloropicrin and chloropicrin alone also significantly limited disease in these highly susceptible crops in 2004.
When considering fumigation, it is important to take several
important factors into account. First, fumigation in
In order for the fumigant to work, a moisture seal to lock in the fumigant needs to be present. There are two ways to accomplish this task. A plastic film seal can be applied on the soil surface, or machinery seals are a second option.
Remember that fumigation is not the only strategy for limiting Phytophthora. Field rotations should be adjusted in order to avoid rotating with other Phytophthora-susceptible crops. Irrigate conservatively only with non-surface water sources, and use drip irrigation whenever possible. Avoid moving farm equipment between diseased and clean fields without proper cleaning, and never dump diseased plants and fruits onto a field. Apply fungicides early and often, and most importantly, scout fields continuously for any sign of disease.
Amanda
Gevens, Brian Cortright, and Mary Hausbeck,
Plant Pathology
Powdery mildew is perhaps one of the easiest diseases to
identify because of the whitish, talcum-like, powdery growth that develops on
leaf surfaces, petioles, and stems.
Infected leaves usually wither and die. Premature loss of foliage often
reduces the size or number of fruit and the length of the harvest period. In
addition, powdery mildew infection predisposes plants to other diseases such as
gummy stem blight. Powdery mildew occurs each year, although the time of
disease appearance is unpredictable.
Propagules responsible for infection (conidia or spores) may be
transported rapidly over long distances by air currents. Therefore, the disease
may become established in a clean field from conidia blowing in from a field
affected by the fungus. It is also
possible that this disease may overwinter in soil and plant debris in a hearty,
weather-resistant fungal structure (cleistothecium). Although this has not been verified for
Once powdery mildew is present, the disease can increase rapidly. The fungus can multiply and spread quickly under favorable conditions because the length of time between infection and symptom appearance is usually only three to seven days. Also, a large number of conidia that can infect healthy tissue can be produced in a short time, and contribute to spread of the disease within a field.
Currently, fungicides are the primary control practice for
this disease. Resistant cultivars are
becoming more widely available. Many
products were tested for their ability to control powdery mildew (Figures 1 and
2). To avoid the development of resistance, fungicides should be used in
alternation. Since
It is critical that a field be monitored closely for the first appearance of the disease. To monitor effectively, a grower must walk through a field once or twice a week to look for powdery mildew, especially on the older, shaded leaves. Do not forget to look at the underside of the leaves. It is apparent from field observations that early control of powdery mildew is the most effective.
Downy mildew was confirmed in
Downy mildew is well-known for causing catastrophic losses
of cucurbits in a brief period of time.
When it is overcast, cloudy, and humid, unprotected foliage can become
completely infected and appear to be frosted within 10 days of infection. The pathogen appears to have come to
Currently, there are few cultivars with adequate resistance to downy mildew. Chemical control must be focused on using the most effective products, alternating the products, and applying the fungicides at short intervals. Results from our 17-product downy mildew spray trial indicated that the most effective spray programs include the following: Previcur Flex (propamocarb hydrochloride, Bayer CropScience) plus Bravo (chlorothalonil, Syngenta Crop Protection) alternated with Tanos 50DF (cymoxanil + famoxadone, DuPont Crop Protection) plus mancozeb (or Tanos + Bravo). Our study was conducted in a young pickling cucumber field that was already showing early downy mildew symptoms and sporulation. Overall, fungicides are more likely to be effective when applied prior to the appearance of the pathogen. Previcur Flex is a critical component of the fungicide program. It appeared to be especially effective and offered a different mode of action from that of Tanos 50DF. Tanos 50DF has a three-day PHI and Previcur Flex has a two-day PHI. The addition of mancozeb increases the PHI to five days. Bravo has a zero-day PHI. In addition to fungicide application, it was recommended that any infected vines remaining after harvest should be killed with an herbicide or plowed under immediately so that they do not serve as a source of downy mildew for nearby crops. In a 43-acre pickling cucumber field with initial downy mildew infection at the first true-leaf stage, the recommended Previcur Flex spray program turned the field around to yield 170 bushels per acre.
Figure 1. Evaluation of fungicides for managing powdery mildew for pumpkin in 2004. Figure 2. Evaluation of fungicides for managing powdery mildew for pumpkin in 2005. Figure 3. A) Downy mildew symptoms on the top of a cucumber leaf (note angular yellow spots). B)
Downy mildew symptoms on bottom of cucumber leaf (note gray, fuzzy, dirty sporulation).
Ron Goldy
Temperatures during the week were generally near average (82oF) with highs of 79oF to 87oF and lows from 57oF to 70oF. The area received a break from rain with only near 0.2 inches. Daily humidity averaged near 80 percent.
Diseases in general have made a big increase over the past week and have caused quality issues in many crops. Phytophthora can be found in pepper, squash, and pumpkin fields and is suspected in snap beans and tomatoes. Bacterial spot and speck has increased in tomatoes. Powdery mildew can be found in many vine crop plantings. Virus symptoms are increasing in vine crops and peppers.
Cucumber beetles are still active. Squash vine borers are at zero and squash bug populations appear low.
Bill Steenwyk
Rainfall varied from 0.1 to 0.75 of an inch this past week.
Celery continues to look good, with harvest continuing.
Early onions are ready for harvest.
Many cucurbit and cole crops are being harvested and shipped. Other fields have recently been planted. Many pumpkin and squash fields are ripening sooner than normal. Growers may want to protect fruits from rotting in the fields with fungicides.
Tomatoes and peppers continue development, with some foliar and fruit diseases taking hold.
Sweet corn harvest is approximately fifty percent complete. Overall, the crop looks good, but in some instances, ear size, tip fill and husk scald issues affect marketability.
Norm Myers
The weather has continued to be dry this past week, with only brief showers. Irrigation continues to be general, with many growers nearing the end of their energy or their water supply.
Asparagus fern continues to show signs of drought dormancy
on the very light soils. We also
continue to see die-back of fern from phytophthora in many fields, especially
older,
Keeping up with irrigation continues to be the main concern of most carrot growers. All of the usual diseases, plus bacterial wilt are present in fields.
Pickles/cucumbers still report no signs of downy mildew. I have looked at a number of fields, but all I have seen so far is drought damage.
Green zucchini yields continue as normal, but we have noticed a huge up swing in fruit abortion on the yellow variety that we grow for processing. We are unsure of the reason for this, but it is being investigated.
Our usual powdery mildew control program does not seem to be working this year on winter squash and pumpkins. The strobi fungicides seem to be having no affect on the disease. Whether this is a new resistance or some other problem we are not sure yet.
In sweet corn and snap beans, corn earworm catches jumped this last week to 12 moths. We are still not catching any European corn borers.
Jim Breinling
Carrot harvest is
now in full swing with fresh market and cut-and-peel plants operating in
Onions continue
to size. I observed one field in
European corn borer trap counts at the snap bean site in
Corn earworm trap counts at the sweet corn site in
There is some acreage of spinach for processing being planted at this time in
Not much difference to report in vine crops other than conditions have been favorable for development of powdery mildew even though rainfall has been minimal, there have been a number of foggy mornings.
Hannah Stevens
There have been a couple of brief rain events this week, but the region is still profiting from last week’s rainfall, with the exception of some areas that had water damage. High temperatures have ranged from the mid-eighties to the mid-nineties with several days of high humidity.
Sweet corn benefited greatly from last weeks moisture. Growers are having the perennial problem in a good growing period of having corn “bunch up” with later varieties or plantings coming in earlier than expected. Thus, there is some concern with having too much corn now and not enough later. I believe we will notice an improvement in both quality and appearance of later corn, due to recent moisture. European corn borer flight seems to be well into the second generation and one corn earworm appeared in the trap last week. I have also seen small larvae of both species in the ears of unprotected corn.
For vine crops, now is a good time to walk pumpkin fields to see what the yields will be. If there is one fruit per plant on 4.0 by 6.0 ft. spacing, the yield will be about 1800 fruit per acre. Take a scale out to measure the average weight and you have the tonnage. I think we will have quite a variation in yields this season.
There are a few spaghetti squash on the market. Seeded and seedless watermelons and muskmelons are of good yield and quality from what I have seen. Slicing cucumbers also look very good. Powdery mildew is in full force where the fungicide program is behind or perhaps not effective. If the rates and interval are correct, there may be a resistance problem with the systemic materials and I would like to hear about that.
Some onion fields have been rolled and some are being dug. Carrot harvest is well underway, and the roots are exceptionally long and tender.
Tomato fungicide programs are really important at this time to prevent foliar disease from taking hold. If there is still a problem despite a good program, this might be bacterial disease. This can be diagnosed for planning next year’s program. The easiest route is through your county extension office to MSU Diagnostic Services.
Thursday, August 23, 2007
George Van Houtte Farm,
For producers:
3:00 Walk watermelon, muskmelon and tomato plantings with MSU specialists.
5:00 Sweet corn plot viewing and discussion (16 SE and 7 SH2 bicolor cultivars).
For producers and their customers (Only invite selected customers please. Do not distribute.)
6:00 Sweet corn taste and quality evaluation and light dinner.
7:00 Innovators and entrepreneurs club meeting.
8:30 Adjourn.
If you need more information or directions, please give me a call at 586-469-6440.
Paul Marks
Rain over the last seven days has been limited to several events which provided between 1.0 and 2.0 inches of moisture. Temperatures have been in the low to mid 80’s during the day and low 60’s at night. Much higher humidity and longer periods of wetness in the morning has increased pressure from fungal pathogens. All crops have responded to the moisture of the last two weeks with tremendous growth. We have gone from a period of moisture shortage to now having fields with water damage! Many growers have not been able to keep up with spray schedules due to rain and wet soils.
Processing tomato harvest has begun this last week. Market tomatoes are in large supply with good quality packs being marketed. Both of these crops have increased alternaria infestations.
Potatoes continue
to be harvested on an as need basis for market.
Alternaria early blight has increased in many fields over the last
several weeks.
Sweet corn harvest is continuing with later planted non-irrigated fields now looking much better due to rains over the last two weeks. Corn borer trap catches were very low again this week averaging about one per trap while the numbers of corn earworms increased dramatically to as many as 14 in one trap. Some limited rust is now in this crop.
Pumpkins and hard squash have made a lot of growth over the last two weeks with fruits now showing in most fields. Some color is showing in earliest fields. Powdery mildew has increased again this week in many fields.
Cucumbers continue to be plagued by downy mildew as do some muskmelon fields.
Cabbage and other cole crops for fall harvest are developing very quickly now. Worm pressure appears to have increased, and even fields with a good spray program have a few visible holes in leaves.
Jeff
Andresen
Agricultural Meteorology
Geography
A cold front will move across
Temperatures during the next few days will fall back to
below normal values, with highs ranging from the mid 60's far north Friday to
the upper 70's far south and lows from the low 40's north to upper 40's south
through Sunday. Warmer temperatures are
expected by early next week, with highs returning to the upper 70's to low 80's
across most of the state. A warm front
is forecast to approach from the southwest by Sunday, bringing a chance for
rain by late in the day or on Monday.
Rainfall amounts and coverage early next week could be significant
should remnants of Tropical Depression 5 (which could become Tropical Storm
Erin) move northward from the western Gulf of Mexico into the
Next week, the jet stream flow across North America is
expected to remain a bit more zonal (west to east) than has been the case
recently, resulting in more frequent chances for precipitation, and this is
reflected in the new 6-10 day outlook.
Both 6-10 day and 8-14 day outlooks, covering August 20-
24 and August 22-28, call for a
continuation of above normal temperatures statewide. Precipitation totals
during the 6-10 day time frame are forecast to increase to above normal levels
statewide. In contrast, precipitation totals during the 8-14 day period are
expected to fall back to a range from below normal levels across the Lower
Peninsula to near normal levels in