Weed management strategies with Picea abies L. sawmill by-products

Weeds can cause significant impact on agriculture and require effective management; however, traditional control measures can lead to serious environmental damage. Considering both the need and demand for more sustainable use of pesticides in Europe, regenerative bio solutions are gaining much attention, especially the possibilities for by-product usage. Here, such a possibility was examined using sawdust and bark from Picea abies L., the most common conifer in the Alpine region forestry, known for generating large quantities of these by-products in sawmills.

The tests comprised the assessment in Petri dishes of phytotoxic effects on germination and root growth of two weeds Abutilon theophrasti Medik. (ABUTH), Lolium rigidum Gaudin (LOLRI) and two crops Triticum aestivum L. (wheat) and Sinapis alba L. (mustard) treated with P. abies bark and sawdust aqueous extracts at different concentrations (from 0 to 100% v/v). Another test was carried out in pots to evaluate the effects of these by-products as mulches and phytotoxicity by incorporation in the first 10 cm of soil. For this trial, Amaranthus retroflexus L. (AMARE) and Glycine max L. (soybean) were added to the species used in the Petri test.

The by-product incorporation test showed no germination reduction but increased AMARE germination by 9%. This corresponds to the Petri tests where no effect on germination was observed. Regarding root elongation, sawdust extract shows no relevant effects except for 35.3 % reduction in mustard root growth at the 100 % v/v concentration. Bark extracts were more effective, particularly at the highest extract concentration (100 % v/v), reaching root growth reduction from 41.8 to 69 % for all species. The most susceptible species was LOLRI with root growth reduction by 44.5 and 69 % at concentrations of 40 and 100 % v/v, respectively.

Conversely, bark and sawdust mulching effectively reduced germination in species with smaller seeds (-51% in AMARE and mustard, -27% in LOLRI), while having little or no effect on the others. In addition, mulching delayed emergence of all species by no more than one day compared to untreated. LOLRI and ABUTH showed the most significant germination slowdown with an average of 35% at the higher mulching dose of 2.25 kg/m².

As an innovative solution, the use of sawmill by-products as mulch seems to be the most viable strategy for sustainable weed control and increasing its use is desirable considering the environmental benefits. Results suggest that the mulching effect is purely physical, while releasing allelopathic compounds from by-products does not affect the species germination. The development of natural herbicides from waste bark and sawdust has not yielded satisfactory results, but the presence of phytotoxic compounds, especially in bark extracts, is suspected. Chemical analyses may be carried out to assess their presence.