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Eastern New York Field Crops Pest Report, 2004

This is a seasonal scouting report giving growers in the Eastern New York area information on the presence of agricultural pests. The report is written by Ken Wise, IPM Extension Area Educator for Livestock and Field Crops.

July 16, 2004

Why use Potato Leafhopper Resistant Alfalfa?

Have you had problems with potato leafhoppers (PLH) in your alfalfa? You know that large infestations of PLH in alfalfa can reduce the plant protein by 5% and yield by a half ton per acre per cutting. If you see V-shaped yellowing on the tips of the leaves you have a good chance potato leafhopper has been in your alfalfa. If V-shaped yellowing has appeared you have already lost protein and yield, plus the alfalfa will have slower re-growth after harvest and increased chance of winter kill. A good option for reducing losses to this insect pest is to plant PLH resistant alfalfa. Research has shown that potato leafhopper resistant alfalfa is consistently higher in quality than susceptible cultivars with or without potato leafhopper pressure. Some of the most recent releases of PLH resistant alfalfa are as high as 70 percent resistant. (Note: a “ highly resistant” cultivar is 50% or more of the plants are resistant.) The newer potato leafhopper resistant varieties have comparable yields as susceptible alfalfa. You will still need to monitor this alfalfa because resistant does not mean that it is immune to the pest. In the first 3 to 4 weeks the young plants have not developed their resistance to PLH. The resistance is the granular hairs that grow in the surface of the leaflets. In the young plants these hairs do not become fully functional until about a month of growth. For management information check our on-line IPM guides: IPM for Potato Leafhopper in Alfalfa.

Field Corn
Common smut on corn or on your plate?

While looking for pests to discuss during a TAg meeting in Lewis County this week we found some common smut on field corn. Common smut looks are white, soft galls that can be found on most any plant part on the corn plant above the ground. It is suggested that the galls form where hail or machinery have injured the plant. As the smut galls age they fill with dark brown to black spore masses. The good thing is that smut rarely kills the plant, and typically causes little if any yield loss. For pictures view this website: Common Smut

Corn smut is also edible at the right stage of growth. It is called the maize mushroom (Cuitlacoche) or the Mexican truffle. Many people in Mexico eat the immature smut galls as a delicacy known as Cuitlacoche. Some sweet corn growers produce smut galls as a high value crop and sell them to Mexican restaurants. If you like mushrooms you should like common smut. Check out this website if you think you would like to try maize mushrooms: Common Smut Recipes

Do you know how to scout for Corn Rootworm?

You will need to scout all corn fields that will be kept in corn next year from emergence of the tassel until pollination is complete. Pollination occurs for three weeks and monitoring takes about 20 minutes per field. You will need to monitor each field once a week until you reach a threshold or until pollination is over. Look for gravid, (i.e. mature, egg laying) corn rootworm females beetles--the ones that, when you squeeze their bodies, release white eggs from their posteriors.

Here’s how you scout:

  1. Are female beetles present? Mature and capable of egg laying? Conduct the squeeze test (see above) to determine if they are ready to lay eggs.

  2. Approach a corn plant carefully because the beetles will fly off if they disturbed too much.

  3. Grasp the silk with one hand.

  4. Count the beetles on the entire plant.

  5. Start counting at the top working down.

  6. Gently pull leaves away from the stalk so you count any beetles that may be hiding in the whorls.

  7. For each corn plant monitored, record the total number of beetles observed. See the sequential sampling chart below. Since western corn rootworms are potentially more damaging than their northern cousins, count each western (yellow striped) beetle observed as “one” and each northern (green type) as “1/2”.

  8. Check several plants at random (not next to each other!) in several parts of the field.

  9. Continue sampling at seven-day intervals until the ear silks are brown, approximately 3 weeks after tassels are first visible, pollination is complete or an above threshold number of beetles are found.

Using the Sequential Sampling Card for Corn Rootworm

  1. Keep a running total (RT) of the number of corn rootworm beetles you have counted on each plant. Each northern corn rootworm has half the value of each western corn rootworm. The western corn rootworm does twice the damage to corn than does the northern. So if you count 3 westerns and 4 northern (2 western equivalent) on a plant you would have a total of 5 beetles.

  2. If the number of corn rootworm beetles observed is smaller than the “N” (“Not at threshold”) number stop and scout 7 days later.

  3. If the number of corn rootworm beetles observed is larger than the “T” (“At threshold” or “Treat”) number then you need to manage rootworms next year.

  4. If the number of corn rootworm beetles observed fall between “N” and “T”, continue sampling additional plants until you finally go over or under.

  5. In a very low or very high rootworm population a sampling decision can be made in sampling as few as 3 to 8 plants. For moderate populations more samples may be necessary to insure accuracy.

Sequential Sampling for Corn Rootworm

Plant N

T

RT

Plant N

T

RT

Plant N

T

RT

Plant N

T

RT

1

        15 7

23

    29 20

36

    43

34

50

 

2

        16 8

24

    30 21

37

    44

35

51

 

3

 

11

    17 8

25

    31 22

38

    45

36

52

 

4

 

12

    18 9

26

    32 23

39

    46

37

53

 

5

 

13

    19 10

27

    33 24

40

    47

38

54

 

6

 

14

    20 11

28

    34 25

41

    48

39

55

 

7

 

15

    21 12

28

    35 26

42

    49

40

55

 

8

0

16

    22 13

29

    36 27

43

    50 41

55

 

9

1

17

    23 14

30

    37 28

44

    51 42

55

 

10

2

18

    24 15

31

    38 29

45

    52 42

55

 

11

3

19

    25 16

32

    39 30

46

    53 43

55

 

12

4

20

    26 17

33

    40 31

47

    54 44

55

 

13

5

21

    27 18

34

    41 32

48

    55 54

55

 

14

6

22

    28 19

35

    42 33

49

           

N= No Treatment

T = Treatment

RT = Running Total

For more information on corn rootworm checkout our online publication: Corn Rootworm Management in Field Corn

Weed of the Week: Wirestem Muhly

Wirestem Muhly is a warm season perennial grass. It is native to the North America and has become problematic in field corn in certain areas of NYS. The grass spreads by short and scaly rhizomes. The stems are 2 to 3 feet in length, smooth below joints, very tough, leafy, branch freely, and often root at the lower nodes. Leaves are flat, rough, pale green, scattered along the stem, and dense near the tip, giving the plant a brushy appearance. The panicle barely protrudes from the leaf sheath. This weed normally starts as scattered clumps in a field and will spread over time. The problem with wirestem muhly is that only glyphosate products can control this weed. This limits your choices to using glyphosate resistant corn plus glyphosate or rotate the field to a different crop. One thing you need to think about is not transferring the weed around your farm. If you have wirestem muhly make sure to clean tillage equipment before working a field that is free from the weed. The rhizomes can be transferred on tillage equipment from field to field. For pictures of the weed view this website: Wirestem Muhly

Soybeans

Soybean Aphids Low across the Country

I have not seen any soybean aphids (SBA) this year. SBA s have been sighted in Western NYS but at low levels. Even in the mid-west SBA populations have been low this season. But you never know what might happen tomorrow? Here are few pointers for monitoring soybean aphids:

  1. The threshold for soybean aphids is 250 or more per plant through the R4 stage.

  2. During pod fill (R5 ĞR6) unless the plants are drought stressed you may need to treat if you have 500 or more aphids per plant.

  3. Count the aphids on the underside of the leaves with an average of 20-30 plants per field.

  4. Aphids will first infest younger leaves.

  5. Do not treat soybeans after the V6 stage.

  6. This threshold allows for about 7 days for treatment action.

For more information on managing insect pest on soybean check out our on-line publication: Soybean Insect Pest Management Guide

Thanks to: Jennifer Beckman (Lewis County) and Keith Waldron and Julie Stavisky (NYS IPM) for contributing to this week's report.

Cheers
Ken Wise