Abstract

In the work results of studies carried out in north-eastern Poland in the seasons 1995 and 1996. The effects of lack of insecticides application on amount and quality of spring rape yield were studied. Variable rates of nitrogen fertilizers i.e. 0; 40; 80 and 120 kg N per ha were applied. In the years of the studies low of abundance of Ceuthorrhynchus napi Gyll. and Ceuthorrhynchus quadridens Panz. was found. Only 0–2% of stems were infested and 0–3% of stems were injured. Meligethes aeneus F. destroyed 39–42% of blooms in treatments without insecticide application whereas this percentage amounted to 31–34% for treatment with full protection, pods pests i.e. Dasyneura brassicae and Ceuthorrhynchus assimilis destroyed 14–19% and 3–6% of pods, respectively.

Desisting of insecticides application resulted in the loss of 14% of yield in the conditions of lack of N fertilization whereas for treatment where 40 and 120 kg N were applied as much as 23% of seed yield was lost. It was found that the spring rape gave yields on the same level when full insecticide control was done and no nitrogen was given and when no insecticide was applied together with 120 kg N. Our results indicate that lack of spring rape protection cannot be compensated by increase of nitrogen fertilizer rate what sometimes is suggested in literature and recommended in practice.

Lack of insecticides application markedly affected quality of spring rape seeds and in treatments with no crop protection 1.7% lower oil content with 1.8% higher protein content was found.

Introduction

The opinion that plants show ability to compensate pest injuries and even in some case they respond to pest injuries by enhanced growth and setting of additional generative organs and higher yield is common in practice and literature (Dmoch 1996, Hurej and Kelm 1986, Lerin 1987, Łęski 1995, Williams and Free 1979). Earlier studies on compensation of pest injuries by winter oilseed rape gave contrasting results (Budzyński et al. 1994, Jankowski et al. 1995). Pests cause visible direct losses in seed yield (yield reduction by 20-45%) and decrease strength of plant response to favourable environmental and agricultural conditions. Spring oilseed rape is infested in the spring by numerous pests which cause more losses comparing to winter rape form.

Our studies were aimed to determine the effects of ceasing insecticide application in the conditions of an application of different nitrogen rates on spring oilseed rape seed yield and its quality.

Materials and Methods

Trial was performed in two factorial design when the first factor was pest control (A – untreated control, B – intensive pest control) and the second nitrogen rate (40, 80 and 120 kg N ha^-1).

Experiment was performed in Experimental Station in Bałcyny (NE Poland) on Luvisol of medium content of available P and K and pH ranged betwen 5.6 and 6.1.

Forecrop in each season was winter wheat. Following rate of P and K were applied: 50 kg ha^-1 P₂0₅ and 80 kg ha^-1 K₂O. Nitrogen was applied as urea in rates according to experimental design and the rate 120 ha^-1 was split as follows: 80 kg N ha^-1 before sowing and 40 kg ha^-1 during blooming. Seeds of double zero oilseed rape cv. Lisonne were sown on 19 April (1995) and on 25 April (1996) at the sowing rate 150 seeds m^-2 in interrows spacing 20 cm. On plots with intensive pest control four time the following insecticides were applied: (Bancol 50 WP, Bulldock 025 EC, Decis 2,5 EC, Fastac 10 EC lub Karate 025 EC), against Ceuthorrhynchus napi Gyll. and C. quadridens Panz. (1); against Meligethes aeneus F.(2); and against Dasyneura brassicae L. and C. assimilis (1) having in mind economic threshold of harmfulness. On the untreated plots no insecticide was applied. All remaining practices were done according to standard rules of proper agrotechnics. Oilseed rape plots were harvested in two stages.

Results

In the spring 1995 and 1996 slight infestation of oilseed rape by Psylliodes chrysocephala L. and stem pests e.g. Ceuthorrhynchus napi Gyll. and C. quadridens Panz. was recorded. At treatment without insecticide control 0.7 to 3.8% of plants were infested by stem pests whereas in treatment with full control this index amounted to 0.2-2.7%. At such a low infestation it was not shown that nitrogen rates affected level of stem injuries by pests.

In both seasons of studies the tendency towards setting of more pods in unprotected plants however differences were not proven (Table 1). The significant increase of pods number per plant on N fertilized plots irrespectively of pest control was found compared to unfertilized control.

Table 1. Total bloom number set per one plant – mean values for 2 years

The abundant occurrence of Meligethes aeneus F. on spring oilseed rape plants was noted. This pest destroyed 38 and 69 blooms on unprotected plant in 1995 and 1996, respectively. Insecticides application reduced number of injured blooms to 29 and 26 in 1995 and 1996, respectively. The pronounced differences in per cent of injured blooms under effect of application variable N rates were not found (Tab. 2)

Table 2. Percentage of injured blooms by Meligethes aeneus F. – mean values for 2 years

Pod pests in protected plots injured 5-8% and 2-5% of pods in 1995 and 1996, respectively whereas in unprotected treatments these values amounted to 20-29% and 4-15%, in 1995 and 1996, respectively. The relationship between nitrogen rate and a level of pod injuries was not found (Table 3). It is consistent with Dmoch’s (1996) results who reported that high compensation ability oilseed rape was observed only until the stage of full flowering. It was also reported that injuries made by stem pests and rape blossom beetle might be compensated whereas compensation of injuries made by pod pest even at optimal conditions is very limited.

Table 3. Percentage of injured pods – mean values for 2 years

The ceasing of insecticides application resulted in reduction of oilseed rape yield by 20% on an average from 2 years (by 0.48 tons ha^-1. As nitrogen rate increased the value of lost yield increased – when no N was applied 14% of yield was lost whereas in treatments with application of 40 and 120 kg N ha^-1 amounted to 23% (Table 4). Enhancement of seed yield of protected oilseed rape was noted to the rate of 120 kg ha^-1 and for unprotected to the rate of 80 ha^-1. It should be emphasised that yield of unprotected oilseed rape obtained in the conditions of application of 120 kg was lower than yield of protected oilseed rape grown without nitrogen. Nitrogen application did not compensate effects of pests infestation. Obtained results are contrary to Dmoch’s (1996), Lerin (1987) and Williams and Free (1979) reports and confirm our earlier findings for winter oilseed rape (Budzyński et al. 1994; Jankowski et al. 1995).

Table 4. Yield of oilseed rape – mean values for 2 years

In our studies was found that ceasing of insecticides application did not affect quality of obtained plant material (Fig. 1). In seeds obtained from unprotected plots increase of oil by 1.7% was determined but protein concentration was by 1.8% higher comparing to the protected plots. Toboła et al. (1996) who found similar relations in winter oilseed rape explained that injuries made by Meligethes aeneus F. and saddle gall favoured oil accumulation in seeds which number is lower due to pests activity.

Fig. 1. Content of oil and protein in oilseed rape seeds

Conclusions

1. Ceasing of insecticide application resulted in decrease of spring oilseed rape by 20%.

2. Nitrogen application did not compensate pest injuries by unprotected spring oilseed rape.

3. Seeds of spring oilseed rape from unprotected plots contained 1.7% less oil and 1.8% more protein in dry matter.

References

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