Anatomical Differences Between Crop and Weed

The amount of spray retention by foliage after postemergence applications can affect selectivity. This selectivity is usually due to the crop plant’s having a waxy cuticle that repels the spray solution.Examples include onions, peas, cereal grains, Brassica vegetable crops, and conifers. Medium to high spray volumes usually provide better selectivity, and adding an adjuvant can decrease selectivity as a result of enhanced adhesion of the spray droplets. Differences in leaf shape, size, and orientation between weed and crop can provide some selectivity differences. This is most common for controlling dicot weeds in small grain crops (the grain leaves retain less herbicide because of shape, orientation, size, and granular epicuticular wax). Postemergence selectivity can be due to the growing point of the crop being protected from direct contact by the herbicide while the growing point of the weed is exposed. The best example is dicot weed control (growing point not well protected by emerging leaves) in small grains (growing point well protected by the whorls of emerging leaves). The herbicide must not have a high degree of phloem mobility for this selectivitymechanism to work. For more detail regarding the influence of plant morphology on herbicide absorption, see the review by Hess (1987).

Preemergence selectivity can be due to a difference in root morphology between the weed and the crop. Grass weeds usually have a fibrous root system, whereas dicot crops usually have a taproot system. Thus,growth inhibitor herbicides, such as trifluralin, applied to the soil come directly in contact with the growing root tips in grass weeds, but not with those of the deeper-rooted dicot crops. For this selectivity mechanism to be useful, the water solubility and soil binding characteristics of the herbicide must be such that movement isrestricted to the upper soil profile.
Morphology differences within stem tissue of grass plants can provide differences in selectivity. The growing point of many grass weeds (crabgrass and wild oat) are more exposed to herbicide-treated soil than wheat and barley where the growing point is protected inside the coleoptile.

Farmers asked to keep fields clear of foliage

Plants, trees, wheat and other crops of the seasons have begun dropping off their leaves, as the Met office on Monday asked the farmers to collect the decaying foliages to help the standing crops go growing unharmed. "Falling of leaves has started from trees beside wheat & other Rabi crops. Farmers should collect leaves from the crops as early as possible so that normal growth may not be disturbed," the Met office advised the farmers.
It said wheat crop is in early growing stages in most of the rain-crop (barani) areas of the country. "Farmers of barani areas, obtaining crop water through tube wells are advised to schedule the irrigation according to the expected weather in the next 10 days".
Wheat cultivation is in progress in most of the irrigated areas, it said, adding that "the farmers of irrigated areas should irrigate the crop as per requirement due to dry weather prevailing in most of the irrigated agricultural plains of the country. Normally first irrigation is given after 20-25 days after sowing".
Farmers of irrigated plains of Punjab, Sindh and Khyber Pakhtunkhwa are advised to complete sowing of wheat crop before Dec 15 to get maximum yield. "In case of late sowing in December, the recommended varieties should be cultivated to minimise the expected loss in yield," it advised.
Weather is expected to remain mainly dry and cold in most parts of Punjab especially in upper parts in the next 10 days, the office forecast.
In Khyber Pakhtunkhwa, it said mainly dry and cold weather (very cold in upper parts) is expected, however, rain/thunderstorm with light snow over the hills may occur at a few places of Malakand division on Dec 2 and mid of the next week.
In Sindh and Balochistan mainly dry weather is expected, the office said.
In Gilgit-Baltistan, it said, mainly dry/partly cloudy and very cold weather is expected in most parts of the province. However, it said, rain/thunderstorm with light snow over the hills may occur at isolated places on Dec 2 and mid of the next week. The office said weather in Kashmir is likely to remain mainly dry/partly cloudy and very cold weather.

News Source Business Recorder   News Collected: agrinfobank.com Team