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Beresford, R. M . , and M anktelow, D. W . L . 1 994. Economics of reducing fungic ide use by weather-based disease forec:lStS for control of Vemuria inaequalis in apples. New Zealand Journal of Crop and Horticultural Science. 22, 1 1 3- 1 20.

Beresford, R. M . and M anktelow, D.W.L. 1 995. Methods for di sease assessment in apples, i ncluding growth stages, leaf emergence, black spot and powdery mi ldew. Proceedings of the 48th 1\'e\\' Zealand Plant Protection Conference.

pp89-94.

Beresford. R . M., Salinger, M . J., Bruce. P. E . , and Brook, P. J . 1 989. Frequency of

infection periods for Venturia inaequalis i n New Zealand and implications for

fungic ide use. Proceedings of the -!2nd New Zealand weed and pest control

conference. pp 1 59- 1 64 .

Cl ayton, M . ; Amos, N . D . ; B anks, N . H . and Morton, R.H. 1 995. Esti mation of apple fruit surface area. New Zealand Joumal of Crop and Horticultural Science. 23,

345-349.

Cooke, B . K . ; Herri ngton, P .J . ; Jones, K.G. and Morgan, N.G. 1 97 5 . S pray deposit

cover and fungicide distribution obtained on i n tensive apple by rhead

mobile spraying methods. Pesticide Science. 6, 58 1 -587.

Cross, J.V. 1 995. Pers . Comm. Horticulture Rese arch International , East M ai l i ng, England.

Hal l , F.R. 1 984. Evaluation of alternate middle row (ARM) spraying for apple orchards . Research Circular. Ohio Agricultural Research and Development Centre Report 283, 1 7-2 1 .

Hislop, E . C . 1 98 7 . C a n we achieve optimum pesticide deposits? Aspects of Applied Biology 1 4, 1 5 3- 1 7 2 .

Hislop, E. C . and Cox, T . W . 1 970. Local redi stribution of fungicides on leaves b y water. Annals of Applied Biology 66. 89- 1 0 l .

Hol land, P.T. 1 98 8 . A predictive model for pestic i de residues on apples. Report to the New Zealand Apple and Pear Marketing B o ard. 2 1 pp.

S 1 5 1

Holland, P .T . ; Malcol m, C.P. ; Mowat, A.D.; Rohitha, B .H. and G askin, R.E. 1 996. Mode l i n g of pesticide residues o n fruit 11: Persi mmon. Proceedings of the 49th New Zealand Plant Protection Conference. pp 1 92- 1 97.

Lewis, F.H. and Hickey, K.D. 1 972. Fungicide usage on deci duous fruit trees.

Annual Review of Phytopathology. I 0, 399-428 .

MacHardy, W.E. 1 996. Apple Scab : B iology, Epidemiology a n d Management. APS Press. 530 pp.

Mankte low, D.W.L and Beresford, R.J\1. 1 995. Evaluation of an ascospore mon itoring method for Venturia inaequalis to improve appl e black spot fun gicide management. Proceedings of the 48th New Zealand Plant Protection

Confe rence pp78-82.

Manktelow, D. W . , Beresford, R . M., Salinger, M . J . , B ruce, P . E . , and G aunt, R . E .

I 9 8 9 . Use of forecast and monitored weather information for timing apple black spot fungicide appl ications i n Canterbury. Proceedings of the 42nd New Zealand weed and pest control conference. pp 1 65- 1 69.

Schwabe, W. F. S . , Jones, A . L . , and Jonker, J . P. 1 984. Changes i n the susceptib i li ty of developing appl e fruit to Venturia inaequalis. Phytopathology 74, 1 1 8- 1 2 1 .

Smith, F. D . . and MacHardy, W . E. 1 984. The retention and redi stribution of c aptan on apple fol i age. Phytopathology 74. 894-899.

Suckl ing, D . M . 1 98 3 . The responses of Epiphyas postvirrmza (Walker) and

Planorortix excessana (Wal ker) (Lepidoptera:Tortricidae ) to insectic ides . PhD Thesi s : Lincoln Col lege, University of Canterbury. 1 97pp.

Suckl ing. D . M . 1 984. The m inimum effect level concept o f pesticide deposits: A n

evaluation. Proceedings of rhe 3 7rh New Zealand Weed and Pest Control

Conference. pp.59-63.

Szlon i k . M . 1 978. Evaluation of physical modes of action of fungicides against the apple scab fungus. Proceedings: Apple and pear scab workshop. New York Stage Agricultural Experiment Station Special Report Number 28. pp22-27.

Szlon i k , ::v1 . 1 982. Redi stribution of fungicide residues in the protection of

unsprayed apple fol i age agai nst scab . 1 982. Fungicide and Nematicide Tests 38, 1 5 5 .

Tustin, S . 1 995. Pers . Comm. HortResearch, Hawkes Bay, New Zealand. Van der Plank, J.E. I 963 . Plan t Di seases : Epidemics and control . Academic

Chapter 6 1 52

Chapter 6

6

Conclusions

6.1 Spray deposit assessment

Wash-off recovery of water-soluble tracers from leaf and fruit samples proved a rapid, cost effective and practical method of measuring spray deposits. While fluorimetry was identified as the prefe rred wash-off recovery techn ique, i t was possibl e to measure food dye deposits to \vith i n approximately ± 0.05 ).l.g cm-:�. This level of p recision was ea. 1 - 1 0% of typical deposit levels encountered and was considered acceptable given that experimen ts sought to detect relatively large variations in deposits between treatments and/or sample zones . Problems encountered with variable absorbance patterns and recovery rates of food dye tracers could be avoided in the future b y selection of c hromagens (Cross et al. , 1 997) and by testing absorbance l evels on new stock solutions for each major experiment.

Scales at which deposit data need to be expressed were identified as; l eaf surface, whole leaf or fru it, zones with i n trees. and whole trees. Data at the three larger scales could be obtai ned from washed removal of spray tracers . A tree zoning system was devel oped that permitted consistent strat i fied sampling across a wide range of canopy forms and, for most experiments, deposits were assessed u s i n g bul ked samples of leaves or fruit from these zones. An attempt was made to use visual ranking of deposi t distributions to enable semi -quantitative assessmen t of deposits on separate leaf surfaces. However, this proved of l imited use and the q uantitative

separate surface wash ing technique described b y Cross et al. ( 1 997) would be

adopted i n preference for any future work.

Standard methods for presentation of spray deposit data were adopted. Where rel i able c anopy LAI data were avai lable . deposit data could be e xpressed i n terrns of percent leaf spray retention. Deposit data \\·e re considered best e xpressed in terms of micrograms of tracer/chemical deposited per squ are centimeter of tissue surface area (with si ngle surface areas quoted for leaves l for a standardi sed application rate of one kil ogram of tracer/c hemical ai per sprayed hectare. It was recognised that expression of chemical deposit or application rates on the basi s of a standard ground area was an arbitrary conven ience which did not account for variations in canopy area, volume, height, row spacing etc . However, the ground area convention was adopted in prefere nce to others which have been used le . g . c anopy hei ght or emission per metre of travel) because it was unambi guous and i s used i n many areas of sprayer calibration and determ i nation of chemical rate s .

S pray deposit vari ab i l i ty data were considered best expressed as the coefficient of variation (CV) of u ntransformed deposit data. S pray retention \vas identified as an i mportant i ndication of sprayi n g efficiency. which would allow direct comparison of results fr'om differen t sprayi ng experiments. However, spray retention data requi re accurate estimates of crop organ surface areas and the logistical i mpossibil ity of obtain i ng surface area data meant. in many c ases, that spray retention could not be calculated.

Chapter 6 1 53

6.2 Canopy effects on spray deposits

Most New Zeal and appl e canopies are now trained to some variation of an i ntens i ve single central leader system, with single row pl antin gs that show a high degree of along-row continuity i n the lower parts of the trees. Typical tree forms are markedly different from those elsewhere on which most of the published spray applic ation research h as been conducted. It was therefore anticipated that deposit patterns, problems etc on New Zealand canopies would not necessaril y fol l ow those observed in other studies .

S pray retention (spray u se efficiency) o n leaves ranged from 25 to 90% o n seven different c anopies. Leafy, continuous canopies exhibited greatest spray retention, but these factors alone could not be used to predict spray retention i n different canopies. There was a two-fold variation in spray deposits between c anopies fol lowing application of a constant rate of chemical per hectare, with small trees rece i v i n g higher deposits. U s e of t h e tree-row-Yolume (TRV) spraying system t o adj u st chemical rates approxim ately halved deposit vari ations between different tree s izes compared with deposits at a constant chemical application rate per hectare . Deposit trends between canopies were reversed when chemical rates were determined o n the basis of TRY ' s, with small trees recei,·ing l owest deposits. There was some evidence of a non-li near relationship between TRY and deposit fol lowing TRV. Further work would be requ ired to confirm this, but low deposi ts on small trees fol lowing TRV sprayin g could be explained i n terms of low spray retention in small trees with discontinuous canopies.

HS-TRVs measurements, where canopy row-end profi les were estimated from spread measurements at half metre height intervals provided a better estimate of actual tree-row volume than either the US -TRV or HC-TRV systems which assumed rectangular or triangular row-end profi le respective l y . However, vari ations in spray deposits between canopies after (simulated) TRV adjustments to appl ication rates were sti l l undesirabl y high, which suggested that other, independent, factors influenced spray deposit levels. Canopy density was expected to be the key additional canopy feature that influenced deposit levels. Unfortun ately. l i ght penetration and LAD were used as i ndicators of c anopy density and both proved to be highly correl ated with TRY.

Deposit variations between zones within trees were remarkably consi stent between

all but the l ender spindle, canopy . Deposits tended to dec rease w i th

increasi n g distance from the sprayer and/or i ncreasing canopy penetration requirements. Differen t deposit distributions i n the slender spindle canopy were attributed to a poor match between sprayer air assistance volumes and the tree size. It was assumed that spray was blown beyond the canopy areas immediate l y adj acent to the sprayer. With i n -tree deposits varied up to 3-fold following dilute spray applications and by up to I 0-fold following concentrate spray applications . The l arge, but consistent within-tree spray deposit variations across a w ide ran ge of tree forms suggested that ax ial fan , airblast sprayers are poorl y suited to achieving even spray deposits i n most tree c anopies.

Chapter 6

6.3 Sprayer effects on spray deposits

154

The type, setup and operation of sprayers were identified as key factors that c an i nfluence s pray deposits and can al l be control led to some degree b y the sprayer operator. Axial fan , ai rbl ast sprayers dominate the types of sprayers used in New Zeal and pipfru it orchards, so most attention was paid to determ i ning how spray deposit l evels and vari abil i ty in slender pyramid trees were influenced by; application volumes, travel speeds, air assistance leve ls and nozzle output distributions.

Application volumes

A range of appl ication volumes were tested on seven canopies and deposits were found to increase with decreasing spray volumes . These incre ases were attributed to greater s pray retention at lower spray \·oiumes . H igher spray volumes tended to incre ase the total amount of spray l iquid retai ned on a canopy, even though the efficiency w ith which s pray l i quid was retained decreased as spray volume i ncreased. If the same amount of chemical w as applied in different spray volumes, both deposits and deposit variability would be seen to increase with decreas i n g application volume. The decrease in deposits with increasing spray volume was rel ati vely smal l (ea. 5-

I 5 % ), presumably until vol umes were such that l arge amounts of spray runoff occurred. Once si gnificant nmoff occurred deposits could be as l ittle as hal f those achieved at pre-runoff volumes. S i gnificant runoff losses appeared to commence when application volumes were in the range of one litre per 1 1 -7.5 m3 of HS-TV.

Travel speeds and air assistance volumes

Increasing travel speeds from 1 .9 to 8 . 8 km h" 1 was found to significantly increase spray deposits in a slender pyramid canopy and it was hypothesised that the increased deposits were a result of reduced losses from spray projected beyond trees at l ower travel speeds. These results chal lenged some of the accepted understanding of trave l speed effects on spray deposit . but corroborative data were found in the I i terature .

Poss ible interactions between air assi stance volumes and travel speeds ,,·ere not clearly identified, but there was some indication that the 30.000-40,000 m3 h- 1 air assi stance volumes commonl y p roduced by many New Zealand sprayers are not sufficient to project spray l iquid i nto the tops of typical slender pyramid trees.

Spray ourput distributions:

The top fou r nozzle po itions eac h side (representing e a. 40% of the outlet duct each side) of an axial fan sprayer produced relatively high deposits i n the upper two thirds of the slender pyramid trees . This effect was seen both w i th wide angle nozzles produci n g a fine spray and with narrow angle nozzles produci ng a coarse spray. These results highlighted the i mportance of directing a large p roportion of the spray l iquid i nto the tops of the trees. However. the nozzles directed towards the bottom tier of branches on s lender spi ndle trees were seen to be i mportant in achieving coverage i n this region. While further work would be required to confirm these results, they suggest that 60-70% of the spray l iquid should be delivered to the top half of s lender pyramid trees There was also some evidence that the lowest tier trunk zone of slender pyramid trees mi ght be under-sprayed i f a more conventi on al nozzling w as used, where two thirds of the spray l iquid is directed into the top third of the tree.

Chapter 6 155

A irblast versus Tower sprayers: The main tower sprayers sold commerc i al l y in New Zealand h ave not been rigorousl y tested and rel ativel y l ittle w as k nown about their performance relative to standard airb l ast mac hines or about how within tree spray deposit d i stributions are influenced by travel speeds , head p l acement (where applicable) or spray output di stribution . While of l imited scope, the tests conducted here gave some indication of the variable performance of the differen t types of tower sprayers and how deposit distributions can be greatl y influenced by travel speed. More w ork is required to defi ne operating p arameters for tower sprayers if they are ever to achieve the potential improvements they offer over standard airbl ast machines.

6.4 Biological implications of observed spray deposits

Single applica tions leading to a biological response

Carbaryl thinni ng responses and meal ybug control could not h ave been

from the spray deposit data obtained in the experiments reported. However, the

spray deposit data provided some valuable indications of where spray deposits l i mited achievement of a desired biol ogical response.

In the case of thinning responses to carbaryl , i t was found that standard i ndustry spray mixtures provided best thinning responses at high spray volumes with run off, even though the average deposits were O\ er 40% h i gher in lower volume treatments. It appeared that target wettin g was i mportant in ach ieving a thinning response and that this could be achieved at relatively low spray volumes with the addition of a sui table surfactant.

In the c ase of mealybug control from a l ate dormant i nsecticide app l ication , it was identified that all appl ication treatments had coverage l imitations and that unsprayed refugia may p l ay an important role in mealybug control problems. As with the thinning treatments it was identified that bi ological response was more a function of spray penetration and placement than absolute spray volume .

Combination of spray depos it assessments and biological effect measurements in both of the experi ments greatly facil itated interpretation of both sets of data. Had either experiment relied solely on deposit or biol ogical measurements, the results would h a,·e been difficult to interpret and different, possibl y incorrect, conclusions could h a,·e been drawn. A better rel ationship between deposit data and biological responses m ight h ave been achieved i f differen t of pray its had been used. Where organo-silicone surfactants were used it appeared that some measure of spray coverage and penetration was needed. In the mealybug con trol e xperiment it also appeared that some assessment of the area and distribution of unsprayed regions was needed.

Multiple applications and maintenance of residues

A period of 6 0-90 days from budbreak \\·as identified duri ng which most apple leaf canopy is produced and fruitlets are formed. These new tissues are h i ghly susceptible to black spot infections and their rapid emergence and e xpansion was bel ieved to m ake it difficult to maintain a protectant fungicide cover. Deposit l evels and black spot disease control from two alternative spray schedu l i n g methods were

Chapter 6 156

compared against a conventional spring fungicide programme. The altern ative programmes involved 3-5 day application i ntervals, as opposed to 7- 1 0 day interval s i n the conventional programme. Chemical costs in the i ncreased frequency programmes were held simi lar to those for the standard programme by only appl ying h alf the fun gicide rate per hectare at each application. Appl ication costs i n the increased frequency programmes were held down by either making appl ications to altern ate rows, or by increas i n g travel speeds down every row .

It w as ide ntified that equivalent spray deposits and comparabl e within-tree deposit