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Thursday, 18 February 2021 08:59

Summer Crop Management Tips

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By Wendy Madzura, Head of Agronomy services Seed Co Zimbabwe

Download the February Issue 

In light of the lucrative summer season that farmers have been having it goes without saying that the prospects of a bumper harvest are looming. However, this hope can only come to fruition if farmers are able to employ Good Agronomic Practices to unlock the genetic potential of the crops established. 


During this time of the year farmers who managed to establish their crops at the recommended time under rain fed production have crops that are at different stages of growth with most crops being at pollination and the late vegetative stage. 


However, there are farmers with crops that are in the early vegetative stage owing to late establishment. Today we will discuss he agronomic principles that will make the difference between getting a bumper harvest and getting low yields


Fertilizer management plays a pivotal role in provided the nutrient contents desired by the crop to undergo its critical stages of development. At germination and crop emergence, a crop establishes itself using basal fertilizers especially when the rates applied were guided by soil analysis results. 


At around three to four weeks, the crop is ready to grow vegetatively and build its crop stand (statue) in preparation for the reproductive stage where flowering and physiological maturity occurs. 


It is critical for farmers to avail the right amounts of nitrogen based fertilizers at the beginning of the vegetative stage to allow the crop to reach its full potential. In maize production there are two main sources of nitrogen fertilizer, Ammonium Nitrate (AN, 34.5%) and Urea (46%). The farmer’s choice between the two should be done with the full understanding of the fertilizer to be used. 


AN tends to leach below the root zone when applied during periods of persistent rainfall. When this happens the nitrogenous fertilizer may be washed below the root zone thereby resulting in an unhealthy, stunted looking crop. 


As a result of this farmers are encouraged to split apply AN fertilizer to reduce the incidence of leaching. Urea on the other hand is very unstable and tends to get lost into the atmosphere through volatilization as a result farmers should use urea on wet, swampy soils, during periods of persistent rains. Farmers should cover urea slightly with a bit of soil to reduce its loss into the atmosphere through volatilization and thereby ensure its effective use. 


The use of foliar fertilizers is encouraged as it avails macro and micro- nutrients to the crop that complement the efforts of the standard fertilizers applied to the crop. 


Farmers should seek guidance from fertilizer exports on the best type and time to apply fertilizers to their crops.


Picture above shows different weed control scenarios with the recommended one the far right (IDEAL)

Another yield limiting factor is weed pressure. Weeds can account for yield losses to the tune of 50% to 100% if left unmanaged or if poorly managed. Weed control can either be manual/ mechanical or chemical. The most efficient and modern form of weed control is chemical control (the use of herbicides). It is interesting to note however that some farmers have wrongfully judged herbicides as agents of soil destruction when the actual challenge is the failure to understand the principles of effective herbicide use which are:

·        Crop and herbicide suitability (Type of crop)

·        Weed spectrum (grasses, broadleaves, surges)

·        Stage of growth of the weeds (seedling stage, three to five leaf stage of weeds is ideal)

·        Rotation plan (type of crop to be established)

·        Dilution rates (volume of spray as stated on the label)


In a bid to combine operations farmers at times tend to mix herbicides in one tank mix but this should be done upon consultation with the agrochemical suppliers as some products may not be compatible.

Download the February Issue 

Picture above shows Fall Army Worm and its different stages of growth and damage

In an effort to maximize on the leaf area as well as health of the crop, farmers should scout their fields regularly to enable timeous control of problematic insect pests before economic threshold levels are reached. If insect pests are not controlled on time, they can significantly reduce the surface area for photosynthesis thereby affecting PRODUCTIVITY. One of the most problematic insect pest in maize production is the Fall Army worm which has wreaked havoc in maize production in past seasons and currently farmers are crying fowl over the prevalence of this insect pest in their field. The Fall armyworm should be controlled when it is in its 1st intar of development because at this stage it can be controlled by a wide range of insecticides, however the challenge is that most farmers tend to notice the severity of this insect pest when it has reached the fourth instar of development. During the 4th instar the Fall Army Worm will be fully grown and hidden deep inside the maize funnel thereby making it difficult to control. When the Fall Army worm enters the funnel it produces “fruss” that covers the funnel preventing the insecticide from reaching it. At this stage farmers are encouraged to spray using a high volume spray to penetrate deed into the funnel. Insecticide selection for Fall Army Worm should also be done after consultations with agrochemical specialists as there is a wide range of options that can be used. An example of an effective active ingredient is Emmamectin benzoate which may come in different trade names so be sure to always read and understand the label, least you purchase products with different trade names and yet the active ingredient is the same.


In addition to this farmers should always be on the lookout for diseases as they pose a significant threat to the crops ability to reach its full potential and ultimately the yields. The use of hybrid seeds with inbuilt resistance or tolerance to serious disease can significantly reduce the cost of disease control and thereby increase the profitability (ROI). In maize production the selection of varieties that are resistant and tolerant to Grey Leaf Spot (GLS). Another way to effectively manage diseases incidences before they become significant is to scout regularly in a systematic way that ensures that the whole field is covered. Farmers can opt to use preventative fungicides especially in crops like soya beans to reduce the incidence of rust. Once a diseases has been noticed farmers should use systemic curative fungicides before the disease spreads across new plants

The 2020/ 21 farming season is unique in the sense that the rainfall can persist for our or days on end and this increases chances of water logging condition in the fields that may affect crop growth. As a result farmers should work to ensure that drainage is maximized in the fields and for those farmers establishing horticulture crops or Sugar beans, establishment of the crops should be done on ridges or raised beds to manage drainage. This is particularly true for the establishment of sugar beans. Sugar beans is one of the crops that farmers can establish from mid – January to mid – February and this season this period has coincided with periods of excessive moisture hence farmer should manage drainage for effective production.

In conclusion the 2020/21 farming season is double edged sword. On one end the  rains have brought great home to the farming prospects of rain-fed Agriculture while on the other end the persistent rains have posed challenges in crop establishment, excessive leaching of nutrients and water logging crop stress. As a result farmers are implored on to adjust their cropping programs to maximise on the positive attributes of the season by working on drainage and the application of additional nitrogenous fertilizers when leaching occurs. In farming, there are a thousand reasons for low yields, but only two reasons for high yields: Getting the right germplasm (SEED) and practising GOOD AGRONOMIC PRACTICES (GAP’s)



Read 485 times Last modified on Thursday, 18 February 2021 19:52


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