Primary symptoms
Usually the causes of defoliation are not difficult to identify. Ask the farmer what caused the loss of leaves. Damage due to hail, insects, diseases, and livestock leave characteristic patterns.
The effect of defoliation on grain yield depends on the amount of leaf loss, which leaves are affected, and the time leaf loss occurs.
Confirm the problem by checking below.
Summary
Many factors can cause defoliation (loss of green leaves) in maize. Leaf area is often lost due to insect attack, wind or hail damage, or feeding by livestock. In addition, in many areas farmers remove leaves before the crop is mature to use them as fodder. The effect of defoliation on grain yield depends on the amount of leaf loss, which leaves are affected, and the time leaf loss occurs (Table 10 below).
Is defoliation a problem?
Evidence: observations.
At what growth stage did defoliation occur? If the crop is younger than V4-V5, defoliation will usually have little effect on yield. After the V6 stage, the effect of defoliation on yield increases as flowering approaches and declines with time after flowering.
Estimate the amount of leaf area lost on 5 plants at 10 different spots in the field. If the crop has not reached flowering, observe the top 10 leaves. If the crop has reached flowering, observe the leaves above the ear. Compare the amount of leaf loss and the stage of development with Table 10 below. If the expected yield loss is more than 5%, defoliation is a problem.
Note: If the fodder is an important part of the maize production system, you should not necessarily worry if leaf removal reduces grain yield somewhat. Try writing a budget for the system, including the value of the fodder, and remembering that green leaves tend to be better quality feed than dry leaves. The farmer needs to get the most benefit he can from the system, and in this case he may be willing to lose some grain in order to harvest more or better fodder.
Causes of defoliatoin
Usually the causes of defoliation are not difficult to identify. Ask the farmer what caused the loss of leaves. Damage due to hail, insects, diseases, and livestock leave characteristic patterns.
Possible solutions
- Loss due to insects: apply insecticide; use resistant varieties; change tillage, planting date, or rotation to reduce insect populations.
- Loss due to disease: change to a resistant variety; change planting date.
- Loss due to defoliation by the farmer: recommend a shift in the date of leaf removal if necessary.
- Loss due to hail: some varieties (especially highland maize) are less damaged by hail than others. If hail is a frequent problem, it may be useful to change varieties or shift the planting date.
Table 10. The % yield loss associated with different levels of defoliation occurring at different growth stages.
|
Growth stage
|
||||
|---|---|---|---|---|
| Level of defoliation | V6 | V12 | VT | R2 |
| 33% area removed (1) | 3 | 7 | 22 | 10 |
| 66% area removed (1) | 3 | 23 | 50 | 26 |
| All leaves removed (1) | 2 | 40 | 92 | 80 |
| Leaves below ear removed (2) | 2 | |||
| Plants cut off just above the ear (2) | 45 | |||
| 54% area removed, low density (3) | 28 | |||
| 51% area removed, high density (3) | 18 | |||
| 73% area removed, high density (3) | 37 | |||
Sources:
(1) CA Shapiro, TA Peterson, and A.D. Flowerday. 1986. Yield loss due to simulated hail damage on corn: a comparison of predicted and actual values. Agronomy Journal 78:585-589. (Temperate maize)
(2) 2 R.F. Soza, A.D. Violic, and V. Claure. 1975. Maize forage defoliation. Paper presented at the XXI PCCMCA Meeting, EI Salvador. (Tropical maize)
(3) G. O. Edmeades and H. R. Laffite. 1993. Defolation and plant density effects on Maize selected for reduced plant height. Crop ScL in press. (Tropical maize; remaining leaves were close to the ear)