Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
Why were my fruit sprays not effective?
There can be several reasons why fruit trees may have blemished fruit even though you are spraying regularly. One of the most common reasons is that the spray was applied too late. Many sprays for both insects and diseases need to be applied as a preventative before the problem is present. In the case of fungus diseases once a leaf is infected the disease in that leaf usually can not be stopped and in time the leaf will yellow and drop. Some pesticides need follow up applications to provide adequate control. Be sure and follow label directions closely.
Another problem can be with pesticide coverage and mixing. Follow label directions for correct rates and mixing. Some sprays need to be agitated or shaken regularly during use otherwise the active material can settle out. It is also important that the plant be sprayed thoroughly. If all parts of the plant are not covered, the pest may still be present in sufficient numbers to cause damage or to multiply and travel to infect other parts of the plant.
It is also possible that the wrong spray material is being used. For example, an insecticide spray for aphids will not control a disease such as apple scab. Make sure the problem is correctly diagnosed if you are unsure of the problem you are trying to control. It is also possible that the problem is caused by environmental factors which will not be affected by spraying.
For more information on fruit sprays refer to Extension publication number 6010, Home Fruit Spray Schedule, available at the Garden's Kemper Center for Home Gardening.