Eric Sideman's Pest Report
July 1st, 2000
Good Morning Growers,
Here is the July 4th weekend edition of the pest report. It is a short one because I am taking a few days off to get the farm in shape, handle strawberry customers until my son gets home from his theatre camp, and enjoy summer. Once a NOFA staff member said to me that she did not have time to enjoy summer. If that is something you have thought, stop a minute and look around. Ok, back to weeding.
The crops still seem to be growing slowly. They sure are off to a late start. At last the peas are in and the very early new potatoes are ready. The classic New England July 4th dinner is just on time.
WARNING!!!! POTATO LEAFHOPPERS
Potato leaf hoppers are here. Check you beans and potatoes. It seems to me that it is going to be a bad season. Go back to the last issue of this pest report for details on controlling the pest or get back to me for more details.
Cucumber beetle
The cucumber beetle is still active. Remember to spray early in the morning for this pest before they are active and flying around. Crop rotation does a fair job with this critter if you are isolated from other growers.
GREENHOUSE TOMATOES
Grey mold, caused by the fungus Botrytis, is causing serious losses in at least two greenhouses. The problem has become evident during the last week to ten days. The disease gets its name from the fact that it causes a grey moldy growth on plant parts including fruit, leaves, blossoms and stems. Leaves become necrotic. At first glance, the fruit symptoms may be confused with blossom end rot, but the color is tan to grey and the affected area is not sunken as with blossom end rot. Botrytis is favored by moist, humid conditions. Recently, we have had a good deal of wet and cloudy weather which is conducive to this disease. Although the houses are fairly well ventilated, the dense plant canopy keeps the relative humidity high around the leaves.
Moisture management is a key part of managing this disease. Use ventilation and air flow to reduce humidity. Relative humidity should below 90% within the plant canopy. This difficult to achieve, especially with heavy leaf growth. Air movement can be increased by removing older leaves below the lowest fruit cluster. Food is translocated downward from leaves to the fruit, so leaves above a cluster should not be removed. Other factors such as nutrient management may weaken a plant and increase its susceptibility to the disease. In one severely affected crop grey mold appeared shortly after the onset of boron deficiency symptoms.
Oxidate is a new hydrogen peroxide product that may serve organic growers well. It is not the same as drug store hydrogen peroxide. It kills the pathogen and spores on contact, but that means it has no residual effect. It has to be sprayed on a regular schedule when spores are arriving and germinating.
SWEET CORN
The earliest corn (grown with row cover or plastic) is silking in Mass. Bare ground corn is mostly still in whorl. There are likely to be some gaps in harvest because growers could not plant for long periods, and because of slow germination and growth.
Its time to get corn earworm traps up, since it looks like there is an early flight in Mass.
Any blocks reaching pretassel should be scouted for European corn borer. Look for signs of feeding damage—shot holes in the leaves coming out of the whorl, frass—or for the small larvae (white or gray with black heads) in the florets of the emerging tassel. Spray if 15% are infested with one or more larvae with a Bt product such as Dipel. Early corn varieties move very rapidly from pretassel to silk. It is critical to get sprays on before tassels fully emerge and silking starts, to clean up early ECB infestations effectively. Reports from southeastern Mass. indicate pretassel corn is over threshold in many fields.
Late Blight Alert (repeated from last week because I think it is important)
June 25, 2000
Late blight has been found in Albany County, eastern New York State, on tomatoes. Samples were sent to Cornell and were confirmed to be late blight. Tom Zitter, vegetable plant pathologist at Cornell University, says it is possible the late blight we have found is a "tomato only" strain. Even so, it is highly recommended for growers to have protective fungicides on their potatoes and tomatoes.
Recent and current weather conditions are conducive to late blight. Long periods of high relative humidity and leaf wetness (from rainfall, dew, fog, or irrigation) are very favorable for this disease. The favorable temperature range is very wide, but the disease proceeds most quickly when average (day and night) temperatures are 59-80 degrees F. The higher the temperature, the more quickly disease progresses. The disease can knock down a field in five days if left alone.
It is very important to go out and scout your fields for late blight. Late blight lesions are large, about the size of a half-dollar. In the morning, before the humidity drops, you will see a ring of white spores around the lesion. Lesion color is dark gray to black. Sometimes, if protective fungicide sprays have been applied previously, you will not see the lesions on the leaf but late blight spores can germinate at the axle of the leaf to the stem, turning the stem black for an inch above and below the axle. Check fields regularly, especially in poorly drained areas where high humidity hangs on. If the weather continues to be wet, do a good job scouting your fields. If you see something that you think could be late blight, do not hesitate to call the U. Maine Pest Management Office at 1800 287 0279.
Potatoes
Colorado potato beetle
If you have not sprayed with the appropriate Bt, or hand picked them, or sprayed something else for the leaf hopper, then you are probably seeing lots of damage from the larvae and they are getting large. The Bts do not work well on the large larva (or the adults). If this is a problem for you, then you will have to turn to rotenone or pyrethrum.
Threelined potato beetle
This critter seems to becoming more common in Maine. I have received a report from a grower that the Bt for potato beetle actually kills the adults of this beetle. I do not know and would like to hear from others if they have seen this happen.
The threelined potato beetle is often confused with the cucumber beetle. It is a more reddish yellow and has 3 broad black stripes. It feeds on potatoes and most other related plants such as tomatillos and lantern flowers. The cucumber beetle is only attracted to the squash family. The larva of the threelined potato beetle, which looks like the Colorado potato beetle larvae, has the unusual habit of plastering granular masses of its own excrement over its body.
More next week. Have a good holiday, and remember to make time to enjoy the summer!