Non-Chemical Techniques

Mechanical Weeding. Weeding equipment roots out and removes weeds from the soil. Its use is becoming increasingly widespread, with improved effectiveness, on row-cultivated crops, including winter cereals, vineyard and orchard crops.

The hoeing machine may be tractor-mounted or pull type. Tines or rotary hoes are fixed to the frame and penetrate the upper crust of the soil (≈ 5 cm deep) uprooting weeds from the soil portion between the rows. The treatment is effective on dry, compact soil, and a stable working depth is maintained by small wheels. Hoeing is usually combined with banding applications of herbicides in the pre- and post-emergence stages. Rows treated may vary from 2 to 8 and speeds from 2 km/h to 8 km/h.

Blade cultivators are equipped with spikes that terminate with a horizontal blade, often tine or ducksfoot shaped. These operate between rows, breaking the upper soil crust, and at a depth ≤5 cm beneath the surface, cutting weed roots and rhizomes. A similar cutting effect is obtained with a vertical disk weeder. Care must be taken in setting the operating distance from the crop to avoid damaging its root system. These types of implements also are used for operating along the tree rows in orchards. Special sensing devices detect the presence of a tree trunk and cause the implement to be shifted to the side, so that it can circumvent the plant.

Figure 1.241. Brushing machine.

The brushing machine is effective during the early stages of weed development. This implement is mounted on a tractor whose PTO drives a set of robust brushes (15–50 cm wide or more), which rotate on a vertical or horizontal axis (Fig. 1.241). The gap between brushes is adjustable; they operate between rows on the upper soil layer (< 5 cm deep), uprooting weeds and carefully removing their roots from the soil, thereby excluding all possibility of resprouting. Optimal results are achieved with low speeds of rotation, a tractor forward speed of 2–6 km/h, and soil that is not too dry or compacted. A special guard protects the crops from the soil that is removed. The operator must wear adequate protection against the dust that is raised.

Figure 1.242. Manual Weeders.

The light spiked chain harrow also can be used on non-row-cultivated crops. It consists of a set of narrow, flexible, vertical steel bars. The spikes scratch the soil with a pressure that can be adjusted in accordance with the crop’s stage of development. This makes it possible, with careful adjustment, to operate during the pre-emergence stage without damaging the crop. At post-emergence, when the crop is deeper-rooted than the weeds, the best results are obtained in the earliest stages of weed development. Harrowing is less effective on wet or stony soil and is totally ineffective against deep-rooted perennial weeds. An optimal tractor speed 7 km/h and a large working width (6–24 m) make it possible to achieve high work rates.

There also are a number of smaller and simpler traditional tools based on the same principles as the machines described above (Fig. 1.242) that can be manually driven or animal drawn: the single or two-row rotary weeder, the wheel hoe, the three-tine wheel hoe. These are all low-cost types of equipment used on small farms in developing coun­tries; the resulting quality of work is good but they are highly labor-intensive (0.01 ha/h to 0.10 ha/h).

Thermal Treatments. Heat can also be effectively used for weed and pest control. In the flame weeding technique, the area between rows and close to the crop is flamed using a gas burner that advances at a low-medium speed (2–7 km/h). The heat of the flame causes the breakup and subsequent withering of weed tissues. On the ground, the increase in temperature only extends to a depth of a few millimeters. The flame weeding equipment (Fig. 1.243) consists of a boom supporting the burners, a gas (liquid propane) tank and a delivery system.

The best results are obtained on weeds in the early stages of development. If the weeds are advanced, the treatment will require increased fuel consumption. Timeliness is an important constraint on this technique. If disregarded, costs will increase and it may not be successful.

The flame weeding operation has minimal environmental impact, but is too expensive to perform on the entire crop surface (gas consumption 150–200 kg/ha). It becomes economically feasible only when used in conjunction with other operations; flaming being restricted to the area near the rows that cannot be mechanically weeded (gas consumption 20–70 kg/ha).

Soil solarization consists of placing clear plastic mulch over moist soil for a period of 1–3 months during the summer. Solar radiation raises the soil temperature, which inactivates some fungi and kills most weed seeds and nematoda. The treatment is effective if the upper layers of the soil are held at high temperature for a total time τ that is sufficiently long. Typical values are: T = 40°C for т > 50 h; T = 45°C for т > 24 h; T = 50°C for т > 12 h.

Solarization fails if the soil does not acquire enough heat (in fact its use is rec­ommended only in warm or tropical climates) or the soil moisture content is too low. Preliminary irrigation sometimes may be necessary.

The plastic film is laid using tractor-mounted equipment consisting of a frame support­ing a spool and two lateral furrowing discs. The tractor moves at 1.5-3 km/h, unrolling the film from the spool onto the soil, while two cylinders press its edges into the furrow that has just been opened, and then cover it with soil.

Vacuum. Collection by vacuum has proved effective on insects and larvae of sufficiently large size, and in particular on potato beetles and grasshoppers. Tractor-mounted suction equipment has been developed: a hydraulically powered impeller blasts a violent air jet towards the upper part of the plants, while simultaneously generating a suction airflow at ground level. Insects and larvae are blown off leaves and fall onto the ground, where they are collected by vacuum suction. At a forward speed of 5 km/h, collection efficiency is «90% for insects and «80% for larvae. Suction is not effective against eggs.

Biological Pest-control Equipment. A more frequent pest-control practice is inundation with predators and parasites. Biological agents such as predators’ eggs, larvae, mites, ladybugs etc. are commonly supplied mixed with inactive material or organic grit (bran, sawdust, hulls etc.). The mix is often distributed manually by walking workers, who gently shake a discrete amount onto the foliage at regular intervals. Application rates are low, ranging in general from a few dm³/ha to 20–30 dm³/ha of mix.

Equipment for ground and aerial application has also been developed, and performs the following functions: it maintains the homogeneity of the contained mixture, releases the mix at an adjustable rate, protects the biological agents from any consequential damage, and improves on the work rates achievable with manual labor. In general, such equipment consists of a reservoir without an agitation system that is chilled to reduce organism activity. The mixture is metered by a variable-speed electric motor.

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