These authors found that densities as low as 1 weed plant per linear m−1 is enough to significantly reduce crop yield. Beltrano and Caldiz found similar results, caused by different densities of Johnson grass . The latter authors found that 17, 34 and 51 plants∙m−2 of Johnson grass decreased tuber yield by 80%, 85% and 95%, respectively. However, in potatoes, due to the poor competition ability of the crop, when weeds emerged at the same time of the crop up to 54% yield reduction was observed, compared with a 16% yield reduction when weeds emerged three weeks after the crop.Results obtained during the evaluation of pre-emergent herbicides in cv. Kennebec shown that the presence of annual weeds such as Common Lambs quarter and Purslane can cause yield reductions between 11% – 29% when the weedy control was compared with the best treatment . Besides, Hutchinson,also determined for the variety North Norkotah -which has a low competitive ability, a critical period from 10 – 24 days after emergence where the crop should remain free of weeds to only suffer a yield reduction not greater than 5%.
Initial weed competition can decrease yield, while competition at the end of crop cycle, such as the one exert by Pigweed,Common Lambs quarter, Bermuda Grass and Field Bin weed could not only reduce yield but could also interfere with harvest operations As already mentioned, in Argentina, availability of selective herbicides to apply in potatoes are limited, being the post-emergence period the more critical in this regard, mainly when broadleaf weeds are considered . Herbicides registered to use on the potato crop are Fluorochloridon, Linuron, MCPA, Rimsulfuron Trifluralin, and Metribuzin , while Flumioxazin is still under the registration process . With this limited number of herbicides available, crop management becomes more difficult as none of this could be used to deal with all weed species. Black thistle, Spiny Cocklebur , Turnip , Cultivated Radish , Common Lambsquarter, Purslane, Annual Vine , Knotweed , Fierce Thorn Apple , Marigold , Pigweed,vertical grow systems for sale and Sunflower can be mentioned as weeds that are control by herbicides registered for potatoes, among others. However not all of these species are controlled with the same effectiveness; for example, Trifularin does not exercise effective control over Turnip and Wild Basil . Metribuzin is the herbicide more commonly used.
It shows excellent control over the majority of the broadleaf weeds, but phytotoxicity has been observed in certain cultivars, such as Shepody and Innovator Besides, several authors have cited weed resistance to this herbicide in areas where it was used in excess Another widely used herbicide is Bentazon, which is applied as a complement of Metribuzin, since control different weeds. For example Spiny cocklebur, Annual vine and Sunflower are controlled by Bentazon and not by Metribuzin, while Knotweed is effectively controlled by Metribuzin, but not by Bentazon. However, Bentazon also showed some phytotoxic effects, depending on the variety Then, within this framework, any new development is desirable, as will increase the options to properly managed weeds affecting the crop, especially if the new herbicides have a broader weed control spectrum. Recently, Clomazone , an herbicide already used in potato crops in other countries has been registered to be used in potato cultivation, in Argentina. Then, the objective of this work was to assess its performance, regarding weed control, crop yield and quality. Since the time this experiment was performed until 2016, the only new herbicide registered in Argentina for potatoes was Rimsulfuron . In general, Clomazone showed an excellent performance, even under low soil moisture conditions, and did not loss activity, as it is the case with other compounds. Besides, absorption of Clomazone is through the apical bud of the weed, which means that it does not require direct contact with the roots to ensure an effective control .
At 45 DAP the following weeds were observed in the trial plots: Spiny Cocklebur, Common Lambsquarter, Purslane, Hairy Crabgrass , and Knot weed. This initial survey showed that weed density can be considered as an intermediate situation when compared with other fields in the Argentinian Pampas . As a general rule, low levels of TE were associated with low CCL at harvest time. When Clomazone 1.6 was applied, TE was higher than for the control treatment, but lower than Clomazone 2.0 and Clomazone 1 + Metribuzin 0.75, which achieved the higher TE. Besides, the increase in TE when the Clomazone rate was increased from 1.6 to 2.0, when applied alone, showed the benefits of increasing the rate. When the combination Clomazone 1.6 + Metribuzin 0.5 was applied the TE decrease compared with the Clomazone 1.0 + Metribuzin 0.75. This shows that it is the right combination of herbicides and rates which improves TE.