MIELIE-INLIGTINGSGIDS | MAIZE INFORMATION GUIDE | 2 0 1 3

CHEMICAL CONTROL

/ iÊ ˆ˜>VVÕÀ>ÌiÊ ÕÃi of regard to nozzles, timely often results in ineffective weed con- application, drift, usage restric- trol and crop damage. Most problems tions, safety warnings, compat- can be prevented by strictly following ibility with other agro-chemicals, label prescriptions. You are com- directions for use etc. pelled by law to do so, as published The efficacy of a pre-emergence herbi- in the Government Gazette. cide, for example requires a fine and Herbicides are “wonder chemicals” even seedbed. Pre-emergence her- as it is used in nature in complex in- bicides must be washed into the soil teractions with soil, extreme environ- (rain or irrigation) before the herbicide mental and climatic conditions and/ is activated. Post-emergence herbi- or in combination with other agro- cides will not be effective if the her- chemicals. What’s more - herbicides bicides are applied when the are killers, supposed to control are under stress (for example drought, unwanted between crop plants. extreme high temperatures etc.) as the herbicide won’t be absorbed effective- To check the efficacy of herbicides in ly by the weed. Beware of drift dur- practice, leave an untreated control in ing the application of post-emergence fields. Such a control is an area of herbicides. Adjuvants to enhance at least 3 - 5 metres, where no her- penetration, adsorption and spread of bicides are applied. This untreated herbicides have to be added to most area can then be compared with the post-emergence herbicides. The pH areas where the herbicides are ap- of tank-water has to be checked and plied. where necessary a buffer and / or am- In finalising your weed control strategy monium sulphate have to be added to please take note of the following: enhance efficacy of post emergence herbicides. Rain or irrigation within six 1. Regular field scouting is important to eight hours after application of post- to identify problematic weed spe- emergence herbicides may wash off cies. the herbicide, resulting in less effective 2. Confirm herbicides registered on weed control. Take note of instructions both the weeds and the crop. with regard to herbicide applica- tion on specific growth stages of the 3. Calibrate herbicide applicators weed. Producers often expect herbi- accurately. cides to provide season long effective 4. Take note of label instructions with weed control, thus up to six or seven

LNR-Instituut vir Graangewasse / ARC-Grain Crops Institute 125 MIELIE-INLIGTINGSGIDS | MAIZE INFORMATION GUIDE | 2 0 1 3 months. Season long weed control ingredient (or mixtures thereof). Grass is unrealistic as environmental condi- weeds that can be difficult to control tions are seldom optimal. For effective will be accentuated on the label and weed control during the whole season usually dosage rates are revised to en- a minimum of two herbicide applica- sure effective control. Positive identifi- tions are recommended. Where crop cation of weeds is therefore the basis rotation is practiced, take note of the of an effective chemical control spray label instructions with regard to wait- program. ing periods for follow up crops.

The control of grass weeds in maize À>ÃÃiÃÊ Ì >ÌÊ “>ÞÊ LiÊ `ˆvwVՏÌÊ (a grass itself) is one of the producer’s ̜ÊVœ˜ÌÀœÊÉÊÀ>ÃÃiÊÜ>Ìʓœiˆ - largest challenges. A disadvantage ˆŽÊLi iiÀL>>Àʎ>˜ÊÜiià is the season long germination of grasses. Early season grasses can be esculentus (Yellow nutsedge/ controlled by pre-emergence gramini- Geeluintjie) cides (grass herbicides). Due to com- Cyperus rotundus (Purple nutsedge/ petition, grain contamination and Rooiuintjie) grass seed present in the soil seed bank, late germinating grasses may Digitaria nuda (Naked crabgrass) still cause problems in the current and (Goose grass/ subsequent seasons. Annual grass Jongosgras) weeds may be controlled by mechani- cal weeding or by the split applica- Sorghum halepense (Johnson grass/ tion of graminicides. Post-emergence Johnsongras) graminicides have also been regis- Urochloa panicoides (Herringbone tered on maize and is usually used in grass/Beesgras) a spray program with pre-emergence Cynodon dactylon (Common couch/ herbicides at or just after planting fol- Kweekgras) lowed by post-emergence herbicides when grasses are at the 4 to 6 leave Commelina benghalensis (Wandering stage. The larger the grass tufts the Jew/Wandelende Jood) less efficient the post-emergence her- (See photo’s on page 121) bicides will be. The efficacy of a her- bicide depends on accurate, timely application of herbicide(s), but also on a most effective weed control pro- gramme. Each herbicide has a label in which a table of grass and / or broad leaves weeds are listed that will be effectively controlled by the active

126 LNR-Instituut vir Graangewasse / ARC-Grain Crops Institute MIELIE-INLIGTINGSGIDS | MAIZE INFORMATION GUIDE | 2 0 1 3

Cyperus esculentus (Yellow nutsedge/Geel- Digitaria nuda (Naked crabgrass) uintjie)

Cynodon dactylon (Common couch/ Sorghum halepense (Johnson grass/ John- Kweekgras) songras)

Cyperus rotundus (Purple nutsedge/Rooi- Eleusine coracana (Goose grass/Jongosgras) uintjie)

Urochloa panicoides (Herringbone grass/ Commelina benghalensis (Wandering Jew/ Beesgras) Wandelende Jood)

LNR-Instituut vir Graangewasse / ARC-Grain Crops Institute 127