Table 1. Percent of giant ragweed plants with stalk boring insect tunnels and stalk boring insects present in various regions of Indiana and Michigan. N=50 plants per regions. In each field 10 plants were investigated: five plants were less than 1-foot tall and five plants were 1- to 2-foot tall.
Sample Time Region   State Avg.
Cental Indiana Northeast Indiana Northwest Indiana Southwest Indiana

Central Michigan

 Southeast Michigan Southwest Michigan LDS (0.05) IN MI
% Of Giant Ragweed Plants With Stalk Boring Insect Tunnels
Aug 2004 72 79 66 68 40 35 64 18 71 46
June 2005 18 26 24 20 20 18 30 NS 22 23
Aug 2005 84 54 58 88 54 48 70 18 71 57
Aug 2005 84 54 58 88 54 48 70 18 71 57
Sept 2005 88 76 84 94 68 74 64 16 86 69
% Of Giant Ragweed Plants With Stalk Boring Insects Present
Aug 2004 18 16 20 24 10 12 22 NS 20 15
June 2005 12 10 16 18 4 8 18 NS 14 10
Aug 2005 18 28 40 36 8 6 20 26 31 11
Sept 2005 42 24 32 28 38 36 32 NS 32 35

 

Table 2. Percent of giant ragweed plants which survived a herbicide application and showed herbicide injury symptoms in late-season field surveys in Indiana and Michigan. N=50 plants per region.
Sample Time Insect Tunneling Present Region LSD(0.05)
Central Indiana Northeast Indiana Northwest Indiana Southwest Indiana Central Michigan Southeast Michigan Southwest Michigan
%
Aug 2004 No 12 2 12 0 13 25 20 13
  Yes 32b** 28*** 40** 36*** 22 31 5*** 17
Aug 2005 No 4 6 2 0 --a -- -- NS
  Yes 65*** 28*** 38*** 28*** -- -- -- 19

aNo data recorded.
bSignificant difference between plants with and without the presence of insect tunneling: P=*(0.05), **(0.01), ***(0.001) determined by a t-test.

 

Table 3. Influence of giant ragweed height, glyphosate rate and carrier volume, and the presence of European corn borer (EDB) tunneling on giant ragweed dry weight.
Giant Ragweed Height
6-inch 18-inch
Carrier Volume
  10 GPA 20 GPA Pooled Over Carrier Volume
ECB Larva And Tunneling Present
Glyphosate Rate Yes No Yes No Yes No
lb ae/a Dry Weight (% of Non-Treated)
0 93 100 90 100 96 100
0.38 64 81 60 82 92 83
0.75 47 62 44 70 81 73
1.5 45 46 41 55 75 70
LSD (0.05) -----------11----------- ------6------