F ruit grow ing

Apple scab ( Venturia inaequalis)

In 1986 we have tested 7 new fungicides for control of apple scab. M any of the chemicals look prom ising, but they have only been tested for one year, and another year is need ed before the question of approval m ay be decided. Only two o f the new chem icals had a significantly po o rer effect than the o th er fungicides tested. The approved fungicides Rübigan, T opas C 50 W P and Cadol M 63 also had a satisfactory effect. However, the effect of R ubigan on fruit scab was a little poorer th a n that of other approved fungicides. This year C aptan fl. was approved as the first liquid captan com pound.

T he attack o f apple scab in our experim ental orchard at Vindinge was m oderate, w hereas the attack was above average at Edelgave, w here one of the experim ents w ere carried out.

G loeosporium on apple

Captal fl. was approved for control of G loeosporium on apple. Like other C aptan compounds, C ap tan fl. turned out to offer good protection against G loeosporium . Besides, Baycor 25 W P was approved for control of G loeosporium .

Blossom wilt on cherries (M onilinia laxa)

T h e experiments continued on the sam e sites as in 1985. T he attack was very severe. Oktave, R onilan fl. and R ovral Akva fl. had a satisfactory effect.

However, these chem icals have only been tested for one year. T he chem icals which seem ed satisfactory in 1985 turned out to have good effect also in 1986.

Rubigan and B enlate had satisfactory effect both at P ræ stø and Lolland. Baycor 25 WP seem ed a little less efficient on Lolland w hereas Saprol had less good effect at both sites th an in 1985. A m ong the benzim idal com pounds, Topsin M and Benlate h ad a fairly good effect w hereas the effect of D erosal varied somewhat.

Cherry leaf spot (B lum eriella ja a p ii)

Experiments w ere m ade with the varieties Kelleris 16 and Stevns berries. T he attacks on K elleris 16 w ere vigorous and m oderate on Stevns berries. A ll the compounds teste d had a satisfactory effect. T here was no significant difference betw een the chem icals.

4 chemicals w ere approved. This is the first tim e th at any agents controlling cherry leaf spot have been approved.

L eaf rollers

Several experim ents with control o f sum m er fruit tortrix m oths and codling m oths were carried out. T he attacks were weak in all th e experiments. H ow ever, B an 86 was approved as this com pound is produced by m aking a small change in the form ulation of Sumicidin 10 FW whose effect is wellknown.

Biobit, which is a biological agent, showed a b e tter effect than in the previous years. However, th e effect is too low, especially in cold weather, and freq u en t applications are necessary for a good result.

F ru it tree red sp id e r m ites

T h e changing w eather m ade it very difficult to carry out long-term experim ents with fruit tree red spider mites. T he hatching of the w inter eggs took place as norm al, but in m ost experim ents only 1 o r 2 countings could b e m ade before treatm ent, and then the rainy w eather reduced the red spider m ite population considerably. In A ugust we were able to carry out 2 experiments o n a mixed sum m er population. In one experim ent various pyrethroids were exam ined.

T he products approved were: A karstin 25 W P, N issorum 10 WP and T alstar.

T alstar is identical w ith Brigade, and the active ingredient is biphenate.

W ith certain types o f acaricides, treatm ent is recom m ended at a late point in the em bryonic developm ent, i.e. just before o r at the start o f the hatching. D aily observations are necessary in o rd er to find the right tim e of treatm ent. T he hatching tim e m ay even vary in different parts o f the sam e orchard. F o r th at reason we tried to find out w hether early application of Apollo and a n oil em ulsion might give the sam e result. Spraying took place in March, A pril an d at the start of the hatching.

It appears from the results that bo th chemicals are very well suited for spraying som e tim e before the hatching starts, and they can keep dow n the population of red spider m ites for 1 or 2 m onths. T he experim ents will b e continued in 1987.

Apple ap h id

T h ere w ere not m any aphids in 1986. The few vigorous attacks subsided after a few days. Since the pesticides tested had a reasonable effect, but slightly low er than the standard com pound, they will be tested for one m ore year b efo re reaching a decision about approval.

Reduced u se of pesticides for control of pests a n d diseases in fru it trees a n d bushes (Steen Lvkke Nielsen)

Reduced ap p lic a tio n of pesticide for control o f apple scab (Venturia inaequalis)

An electronic fungus warning system was tested. A pplication o f th e curative fungicide b ite rtan o l according to the warning equipm ent saved 4 out of 14 standard preventive applications, and the control of apple scab obtained was the same.

Tests to investigate the possibility o f reducing the dose o f fungicide in the spring, b efo re the foliage was fully developed, w ere unsuccessful, because the approved dose of b itertanol (Baycor 25 W P) is an overdose. A pplication o f half the recom m ended dose during the whole season gave ju st as good a control of the apple scab as th e approved dose.

The influence which th e presence of dew on the foliage may have on the effect of the applications was investigated. No difference was found betw een the am ounts o f fluorescent dye deposited on dew-covered and on dry leaves. N or was any difference found betw een the control o f apple scab obtained by spraying on dew-covered and on dry leaves.

The influence o f th e driving speed on the quality of m ist spraying was investigated. D riving 2 and 3 tim es faster than the optim al driving speed greatly reduced th e deposit o f spray liquid on the trees, although the sam e spray volume was applied regardless o f the driving speed.

Preventive a n d curative chem ical tre a tm e n t fo r control of black c u rra n t leaf sp o t (D repanopeziza ribis)

A sterol-biosynthesis-inhibiting fungicide, penconazole/captan (T opas C 50 W P) was tested to investigate its preventive and curative effect on black currant leaf spot ( D repan opeziza ribis (Kleb.) H ohnel). T he curative treatm ent was started when the first visible symptoms on the leaves w ere observed. T h e curative treatm ent gave a significantly lower control o f the diseases than the preventive treatm ent.

Halving th e dose of T opas C 50 W P and the spray volume at the first 4 sprayings o f th e preventive treatm ents before full leaf coverage and applying full dose and spray volum e at the last 6 sprayings gave ju st as good control o f the leaf spot as applying full dose and spray volum e all the time.

Pear leaf blister mite (P hytoptu s p yri) and plum leaf gall mite (P h ytoptu s sim ilis)

Tests of chemicals for control o f the two gall m ites w ere started at two orchards which h ad suffered from heavy infestations th e year before. T he experim ents failed, however, because only diminutive infestations occurred in 1986.

Blossom blight on cherry (M onilinia laxa)

T ests of chemicals for control of blossom blight on cherry was made in cooperation with E. Schadegg. T he tests are described in his section.

Glasshouse Crops (A. Nøhr Rasmussen)

Chemical control of Western flower thrips (Frankliniella occidentalis, Pergande) on Saintpaulia and Gerbera

D uring 1985 and 1986, 3 experim ents with chemical control o f the W estern flower thrips (Frankliniella occidentalis, Pergande) in Saintpaulia and Gerbera w ere carried out at the R esearch C entre for Plant P rotection at Lyngby. T he experim ents included 13 different pesticides, 8 o f which w ere applied in norm al and triple dosage. T h e sprayings w ere applied with 0.21 liquid p er sq u are m etre.

Generally, the effect o f all the pesticides was insufficient in b o th cultures, with the exception o f Shell B irlane 24 E C , which gave 95% effect in Saintpaulia after 3 applications w ith a 0.16% solution and over 80% effect in Gerbera after one treatm ent.

In Saintpaulia, the best effect of the other pesticides tested was seen with Baythroid 50 E C , Sumirody, M K 0936 (avermectin) and O rth e n e 75 SP. However, their effect varied, so that they had an effect of 80-85% in one of the experim ents, b u t only about 50% in another.

T he o ther pesticides tested, viz. Decis, Egodan P arath io n 35 EC, Fastac, H ostathion, M idol Feni 30, R ipcord and Sumialfa had an effect of 60% o r less.

The m ixture of Sum irody and O rth en e 75 SP increased the effect compared with Sumirody, but the effect was not any b etter than with O rthene 75 SP alone.

It has not been possible to estim ate with any certainty w hat is the harm ful effect of th e pesticides on th e plants.