-2- 



These first-generation borers have begun to pupate. Some moth emergence is ex- 

 pected within the next week, but peak emergence should not occur before the week 

 of July 22, or perhaps the week of July 29. Egg- laying will begin within 2 days 

 following emergence. Only late fields of corn should be affected. 



To determine the need for insecticide treatment, examine the whorls of late- 

 planted corn for signs of leaf -feeding by European and southwestern corn borers. 

 Both insects feed in the whorl. As the leaves emerge, they show regular patterns 

 of circular or elongated holes across the leaves. Also, there is some stripping 

 of the plant tissue, appearing as white areas where the green tissue was eaten. 



If you find 60 percent or more of the whorls with this feeding, it is time to 

 treat. If only southwestern borers are present, as little as 10 to 25 percent 

 of whorl feeding may mean economic damage. One to three insecticide applications 

 may be needed to control an infestation of southwestern corn borers alone or a 

 mixture of both the southwestern and European corn borers. Only one application- - 

 at the most two- -would be needed to control European corn borers alone. 



Egg counts are another way of determining the need for southwestern corn borer 

 control. If you find 25 egg masses per 100 plants, treatment may be profitable. 



We have no Illinois information on chemical effectiveness, since treatments have 

 never been made before. Entomologists in the states to the south and west of Il- 

 linois recommend 2 to 3 applications of insecticides at intervals of 7 to 10 days. 

 Granules are preferred over sprays. Endrin at 0.3 to 0.4 pound per acre per ap- 

 plication is usually recommended. Also, 2 pounds of carbaryl (Sevin) or 1 to 2 

 pounds of diazinon are suggested. Although endrin may be the most effective, we 

 do not encourage its use in the area of Illinois most heavily infested with the 

 southwestern corn borer, because many such fields are near wildlife and waterfowl 

 refuges and fish-bearing waters. 



Do not use ensilage, stover, or fodder from endrin- treated corn. If you use diazi- 

 non, allow 10 days to elapse before using the ensilage, stover, or fodder. No 

 waiting period is required for carbaryl. 



Southern corn rootworm larvae, pupae, and adults (spotted cucumber beetles) are 

 present in some cornfields in the southern half of Illinois. The larvae eat the 

 roots. In some late cornfields, they have tunnelled up into the stalks, killing 

 the heart of the plant. The beetles feed in the leaves and silks of the corn. 

 They will deposit eggs in the soil for another generation or two yet this year. 



Northern and western corn rootworms are developing as anticipated. Pupation 

 has begun in northern Illinois, but eggs are still hatching and very tiny worms 

 can be found. This situation may exist for another two weeks. Damage to roots 

 is now evident in many fields; it will become progressively worse during July. 



In northern Illinois, only late cornfields can profit from basal treatments. In 

 case you find extremely high infestations in earlier fields, you may, in despera- 

 tion, want to try a broadcast application of diazinon, phorate (Thimet) or di- 

 sulfoton granules without cultivation. However, the prospects for effective con- 

 trol by this method are not good, unless timely rains should occur. 



