In Illinois , most cocklebur germinates about the same time as the soybeans and grows 

 at about the same rate. In the South, cockleburs seem to germinate at various times 

 during the season when the soil moisture is favorable. 



When a preemergence herbicide is mixed with dinitro, the dinitro may provide contact 

 activity to control cockleburs then present. The preemergence herbicide may help con- 

 trol some of the late -appearing ones. 



Although you may hear or read about treatments that are popular in other areas, the 

 same treatments would not necessarily work well with our soils, crops, weed problems, 

 and climatic conditions. 



Preplant and preemergence herbicides and good cultivation are still the main lines of 

 attack for weed control in soybeans. Present postemergence herbicides may offer some 

 help in emergency situations; 2,4-DB has been the major one, but even it has seen on- 

 ly limited use in Illinois. 



Some applicators and growers like to try new treatments. Sometimes they are quite 

 satisfied. If you are one who likes to try new treatments, remember to follow la- 

 bel instructions closely and "go easy" on the amount of acreage treated until you 

 have the "feel" of the herbicide and application methods. 



Herbicides for late-planted soybeans are usually not as necessary as for the early 

 plantings . Unless we have considerable rainfall, weeds are not likely to be a se- 

 rious problem in late-planted soybeans. Rotary hoeing and good cultivation may pro- 

 vide adequate control. 



PLANT DISEASES 



i 



SUN SCALD OF CORN i 



The sudden appearance of silvery white areas on corn leaves in the northern two- 

 thirds of Illinois has caused much concern. This is a non-parasitic disease, re- 

 sulting from rapid changes in weather conditions. 



E.K. Wade and P.E. Hoppe, plant pathologists at the University of Wisconsin, de- 

 scribed sun scald in 1961. They pointed out that affected plants could be detected 

 when fields were observed from east to west, but rarely from the opposite direction. 

 Affected plants were found scattered at random in the fields that suffered scald. 



Light-grey to silvery -white lesions may occur on either leaf surface, but rarely on 

 both sides of the same leaf and never directly opposite each other. Most lesions 

 appear about midway from the whorl to the leaf tip, and are as wide as the leaf 

 blade. The line separating green tissue from damaged tissue is always clean and 

 relatively sharp. 



Sun scald can develop at air temperatures in the 40 's, so frost is not considered 

 as the direct cause. Heavy morning dews or rainy periods preceding a dropping tem- 

 perature will help cause the injury. Leaf tissue that is "full of water" and suc- 

 culent is predisposed to scald in bright morning sunlight. Cells collapse and leave 

 air spaces in the tissue, separating the epidermis from underlying leaf tissue. The 

 damage is usually superficial. The probability of serious yield effects are slight. 



HOLCUS LEAF SPOT ON CORN 



Holcus leaf spot on corn, caused by the bacterium Pseudomonas syvingae , has appeared 

 on leaves of susceptible corn in areas that have received moderate to heavy rainfall. 



