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Alternativer til herbicider ved etablering af æbleplantage

Summary

Alternatives to herbicides

Alternative methods as covering the soil with rape straw or black polypropylene may be used without negative effects on quality and yield under the optimal conditions as in the present trial. Mechanical harrowing, cover crops as Tagetes, Medicago (hop medick) or grass reduced yield when irrigation was performed daily, but no negative effects were found when irrigating weekly with the same total amount of water. Cutting the weed could not reduce the competition from the weed at the frequency and method used in the trial, and yield was reduced. Yield was reduced when covering with paper wool, independently of irrigation schedule. Probably competition for nitrogen could be the reason and furthermore the material decayed, thus becoming less efficient the second year.

The air temperature was never below 0° C during the flowering period, and hence, no frost damage on the flowers was observed. Rodent (e.g. mice) damage on trees was a major problem in some treatments, especially with Tagetes and polypropylene mulching.

Earthworms thrived under the rape straw contrary to under black polypropylene and in treatment with harrowing. Coverage and numbers of plant species were highest in untreated control and lowest in herbicide treated plots.

Consumer willingness to pay extra for the apples grown without herbicide was tested in a valuation of non-marketed goods by using a questionnaire. The investigation showed, that the consumers were prepared to pay an additional charge between 2,90 Dkr. and 4,14 Dkr. per kilo of apple, where no herbicides have been used. Estimates showed that some of the alternative methods were cost efficient compared to the use of herbicide, based on calculations from agriculture and under the conditions that the calculations were on a right base.

Background and purpose

Herbicides are used to control weed in the tree row in apple orchards. Some alternatives to herbicides have been developed, but their effects on the fruit yield, quality and tree growth have not been studied so far and have not been used by the growers. Cover crops have been studied, but the competition for water and nutrients among some of the cover crops and the fruit trees has been too big. Mulching is used in other crops as lettuce, but the covering of the soil surface should be stable and economically sound to be useful in an orchard. Mechanical weeding in the tree row will be interesting, when the effect on weed close to the trees is large enough. Hence, there is a need to investigate alternative methods to herbicide and identify the potential of the different methods in relation to yield and fruit quality.

Furthermore it will be relevant to determine the effect on flora and earthworms from the different alternative methods. Earthworms consume leaves from the trees and hereby reduce the infection level of apple scab, which is not a part of the present project.

The alternative methods are believed to increase the expenses for the growers which can be a barrier. Therefore the consumer willingness to pay extra for apples grown without herbicide was tested in a questionnaire.

Hence, the aim of the present project was to test possible alternatives to herbicides and their potentials in relation to effect on yield, quality and on natural flora and earthworms. Furthermore the aim was to evaluate the consumer willingness to pay extra for apples grown without herbicide in connection with an estimate of the expenses using alternative methods.

The investigation

A trial with the cultivar ‘Elshof’ was established as a traditional orchard comparing herbicide treatment with 9 alternative methods, including untreated control, mechanical weeding with rotor harrow in the row, weed cutting by a lawn mower, cover crops as: grass, Tagetes erecta or hop medick (Medicago lupulina), or cover material as: black polypropylene (MyPex), paper wool or rape straw. To identify the effect of irrigation schedule a daily or weekly irrigation was applied in all treatments. The effects of the 9 methods on fruit yield and quality, flora and earthworms were determined in comparison to herbicide treatment in a two-year study. A questionnaire was used to estimate the willingness of the consumers to pay extra for apples grown without herbicide.

Table 0.4. Treatments and analysis.

The main conclusions

The results show that alternative methods as covering the soil with rape straw or black polypropylene may be used without negative effects on quality and yield under the optimal conditions as in the present trial. Mechanical harrowing, cover crops as Tagetes, Medicago or grass reduced yield when irrigation was performed daily, but no negative effects were found when irrigating weekly with the same total amount of water. The lawn mowing could not reduce the competition from the weed at the frequency and method used in the trial, and yield was reduced. Yield was reduced when covering with paper wool, independently of irrigation schedule. Probably competition for nitrogen could be the reason and furthermore the material decayed, thus becoming less efficient the second year.

The air temperature was never below 0°C during the flowering period, and hence, no frost damage on the flowers was observed. Rodent (e.g. mice) damage on trees was a major problem in some treatments, especially with Tagetes and polypropylene cover. Earthworms thrived under the rape straw contrary to under black polypropylene and in treatment with harrowing. Coverage was highest in untreated control and in the Medicago treatment and lowest in herbicide treated plots. In the second year of the trial more plant species were found in plot irrigated weekly than in plot receiving daily irrigation.

Consumer willingness to pay extra for the apples grown without herbicide was tested in a valuation of non-marketed goods by using a questionnaire. The investigation showed, that the consumers were prepared to pay an additional charge between 2,90 Dkr. and 4,14 Dkr. per kilo of apple, where no herbicides have been used. Estimates showed that some of the alternative methods would not cost more than the use of herbicide, based on calculations from agriculture and if the conditions in the calculations were right.

Project results

The results showed that yield and quality of the fruit in treatments with mulching with rape straw or black polypropylene were equal to that in herbicide. The yield in quality I was largest in the two treatments with daily irrigation in comparison to herbicide treatment. At weekly irrigation the yield differences were not significantly different between the treatments. Cover crops as grass, Tagetes erecta or hop medick (Medicago lupulina), reduced yield and quality at daily irrigation, but not at weekly. Paper wool and control reduced yield significantly independently of irrigation schedule. Cutting the weed was not enough to reduce the competition from the weed and the yield was reduced especially at daily irrigation. No frost occurred during the period of flowering, and therefore the effect of covering the soil on frost risk could not be determined in the project.

Fig. 0.2. Fresh weight of earthworm (average and standard deviation) in 6 treatments in 2004 and 2005. Data from the two different irrigation schedules are combined, as there was no significant difference between the schedules.

The mulching with rape straw gave in both years a significant larger weight of earthworms compared with herbicide (Fig. 0.2). Black polypropylene and mechanical harrowing gave a significant lower weight compared to herbicide. The results and differences between treatments concerning number and species of earthworms were similar as that of weight.

Number of weed species was largest in untreated control in both years. A reduction in number was observed from 2004 to 2005 (Table 0.5).

The treatments had a major effect of the number of weed species. In year 2005 a larger number of species was found where the treatments had not been re-established as in paper wool and rape straw. An effect of irrigation schedule was found in 2005, where daily irrigation increased number of species. However, still the largest number of species was found in hop medick and control treatment. The number of species was also large in the treatment with paper wool, but paper wool would probably have to be renewed and thereby minimizing the number of species. Furthermore the paper wool treatment did not reduce the number of species competing with the trees according to the reduction in yield in the treatment. An effect of irrigation schedule was seen in hop medick treatment, where weekly, but not daily irrigation gave a high yield and at the same time a large amount of plant species.

Table 0.5. Number of plant species in average in samples of 0,25 m² in the row under apple trees in 2004 og 2005 in relation to 6 treatment combined with daily or weekly irrigation with same amount of water.

Table 0.6. Covering percentage (%) of vegetation in the row under apple trees in 2004 og 2005 in relation to 6 treatment combined with daily or weekly irrigation with same amount of water.

Consumer willingness to pay extra for the apples grown without herbicide showed, that the consumers were prepared to pay an additional charge between 2,90 Dkr. and 4,14 Dkr. per kilo of apple, where no herbicides have been used. The analysis was done at a sample of 1442 people. The effect of attitude, behaviour and socioeconomic variables on willingness to pay was analysed by regression. Estimates showed that some of the alternative methods would not be more expensive than the use of herbicide, if the conditions used were right. Even without an extra payment the mechanical harrowing and mulching could be competitive to herbicide.  Cutting the weed by lawn mower was not competitive because of a large negative effect on yield, whereas cover crops can be competitive at an increased price.

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Version 1.0 April 2007, © Miljøstyrelsen.