ITU 'I 



COLLEGE OF 

 AGRICULTURE 

 UNIVERSITY OF 

 ILLINOIS AT 

 URBANA-CHAMPAIGN 

 AND NATURAL 

 HISTORY SURVEY 

 URBANA, ILLINOIS 



NSECT, WEED & PLANT DISEASE SURVEY BULLETIN 



rATE/COUNTY/LOCAL GROUPS/U.S. DEPARTMENT OF AGRICULTURE COOPERATING 



FOR IMMEDIATE RELEASE 



No. 18, August 4, 1972 



INSECTS 



CORN INSECTS 



This series of weekly bulletins provides a general look at the insect, weed, and plant 

 disease situation (fruit and commercial vegetables excepted) , along with suggested, ab- 

 breviated, control measures. Each individual should check his own fields to determine 

 local conditions. 



UNWERS»3^f»&pS»GN 



European corn borer moths are starting to deposit small numbers of eggs for the second 

 generation. This egg- laying will extend into September, and egg counts may be low at 

 any one time. Not only are newly emerged moths present but some first-generation corn 

 borer larvae still in the early fields of corn will not pupate and emerge as moths for 

 three weeks. Although counts will be low, the cumulative counts of this extended low 

 level of egg-laying may result in some fields with moderate second-generation popula- 

 tions . 



We are not encouraging control on field corn but fields of sweet corn, particularly 

 late sweet corn , should be checked regularly and insecticides applied where necessary. 

 Make applications when tassel ratio is 30 or more. Dig up a plant and measure from 

 the bottom of the plant to the tip of the longest leaf. Split the plant and find the 

 developing tassel. Measure from the bottom of the plant to the tip of the tassel. Di- 

 vide the tassel height by the plant height and multiply by 100. This will give you 

 the tassel ratio. Repeat every 3 to 5 days as long as the field averages 20 or more 

 unhatched egg masses per 100 plants. For fields already tasseled, apply an insecti- 

 cide to corn if it is 14 or more days from harvest and there are 20 or more unhatched 

 egg masses per 100 plants. 



Corn rootworm adults are now present in numbers in some fields. However, most field 

 corn is now pollinated, and the beetles will not affect kernel set as they consume 

 corn silks. In late-maturing fields do not apply any insecticide to control beetles 

 to aid pollination unless there are 5 or more beetles per ear and less than 50 per- 

 cent of the ears are pollinated. 



Corn earworm numbers on early corn were low in late June and early July in southwest - 

 ern Illinois and remain low over the entire state. At Urbana and adjoining areas, 

 there has been little or no earworm activity. Earworms should begin to increase as 

 a problem in both fresh-market corn and canning corn if they are going to do so. 



For sweet corn, chemicals suggested for control of earworms include carbaryl (Sevin) , 

 Gardona, and methomyl (Lannate) . The addition of 1/2 pound of parathion to carbaryl 

 increases the effectiveness of carbaryl. Parathion should be applied only by experi- 

 enced applicators. 



