Field Crops> Wheat (Triticum aestivum L.)> Weed Control

Weeds emerge with the emerging crop seedlings and if not controlled in the early stages of crop growth these may cause reduction in yield varying from 10 to 40 per cent depending upon the intensity and kind of weeds present in an area.

Wheat field is generally infested from both dicot and monocot weeds. The moajor dicot weeds are: Chenopodium album (bathua), Fumaria parviflora (gajri), Cirsium arvense (kateli), Anagallis arvensis (Krishna neel), Melilotus alba and Melilotus indica (senji), Bicia sativa (ankri), Lathyrus spp. (chatri marri) etc. Monocot weeds include: Phalaris minor, Avena fatua (wild oat), Polypogon monspliensis, Cyperus rotundus (motha) and Cynodon dactylon (doob).

Generally, weeds are eradicated with the help of hoe, khurpt etc. However, no-a days it has become difficult due to labour cost and unavailability of loabour. Now a number of chemical weedicides are available that control the weeds in wheat rather effectively. Most common and effective herbicide to kill all the broad-leaved weeds in wheat field is 2, 4-D. It is available in market under different trade names and each formulation has different amount of active ingredients as shown in Table 4.

The above-mentioned quantity of 2, 4-D should be mixed in about 400 to 600 litres of water for spraying in an area of one hectare. The amount of water may, however, vary according to the type of sprayer in use.

Table 4. Different formulations of 2, 4-D, amount of active ingredients in them and their quantity per hectare for weed control

Note: Information is illustrative and is not the recommendation of the product of a particular firm.

*2,4-dichlorophenoxy acetic acid.

2, 4-D should be sprayed in wheat fields 32-35 days after sowing. This period may be extended to the maximum by one week. But after 40 days of sowing, spray of 2, 4-D is not beneficial because by that time weeds have already done the damage to the crop, secondly, after 40 days weeds become woody in nature and are not likely to be killed easily with the recommended dose of 2, 4-D. When 2, 4-D is sprayed between 25 and 30 days, the ears of wheat have been found to suffer from malformation. Malformation adversely affects the uniformity of seed size and thereby reduces their value as grain and seed. Gappy spikelets result in reduction in total number of grains per head and finally lead to reduced grain yield. While spraying 2, 4-D avoid drift of spray in the adjoining crop fields, because a slight drift of 2, 4-D may spoil the pulse crop like pea, gram, lentil and mustard. It is desirable to spray 2, 4-D, when wind velocity is minimum.

Among monocot weeds Phalaris minor is the major weed in most of the wheat fields. In certain localityies the intensity of this weed is so high that it has become rather impossible to grow wheat crop. This weed belongs to family Gramineae, Genus Phalaris. On an average, each plant produces 10,000 to 30,000 seeds. It emerges with the germination of wheat and resembles wheat seedling, therefore, it is difficult to recognize it in the initial stage. There are few distinguishing features by which Phalaris minor can be differentiated from wheat plants in the field (Table5).

To control Phalaris minor spray Tribunil or Dosanex or Isoproturon at the rate of 2 kg (commercial product) per hectare in 400-600 litres of water 32-35 days after sowing. Spray of Dosanex and Isoproturon will also control wild oat if it is present in wheat field.