Fight against Blight

Fight against Blight Blight Fungicide Application Technology survey and spray coverage demonstrations 4 Report prepared by: Dr Ruairidh Bain SAC Auchincruive June 5

Contents Introduction... 3 1. Application Technology Survey 4 (sponsored by BPC and potatocrop.com)... 3 2. Coverage demonstration (SAC at Potatoes in Practice sponsored by BPC and Syngenta).. 4 3. Coverage demonstration (HAUC sponsored by BPC)... 5 4. Blight Fungicide Application Systems Trial (SAC at Auchincruive sponsored by BPC)... 8 Conclusions and discussion... 12 2

Introduction As part of its Fight against Blight Campaign launched in 3 the BPC instigated in 4 a survey of potato blight fungicide spraying practices in Great Britain. Previously there was little detailed information. The results of this survey were used to guide two demonstrations and trial work into the impact of application methodology on penetration and coverage of the haulm and the control of foliar and tuber blight. This report summarises the main findings. The conclusions drawn from the demonstrations are preliminary because these were not replicated. 1. Application Technology Survey 4 (sponsored by BPC and potatocrop.com) The internet survey was completed by growers who logged on to the potatocrop.com website and completed the questionnaire. The survey supplied information on the most commonly used nozzle types, water rates, sprayer types and spray pressures. Eighty-seven growers took part in the survey. These growers represented 5691 hectares. Ninety-seven percent of those who took part applied blight sprays to their own crops only. The survey indicated that the average number of blight sprays applied to the crops was 9.9 sprays. This fits well with broader market research findings. The range of blight treatments varied from 4 sprays per crop up to 20 sprays with the majority being 8-12 sprays. Sprayer type Twenty different sprayer manufacturers were mentioned in the survey, with the most popular being Hardi (used on 15% of farms) and Knights (used on 14% of farms). Eightyfive percent of the area was treated using conventional hydraulic sprayers, 11% airassisted and 4% twin fluid. Other sprayer types accounted for 1% of the area. The relative use of sprayer types was similar for the four main growth stages (rosette, rapid haulm growth, full canopy and senescence). Nozzle type, spray quality and water volume The main results from the survey show that only 14% and 21% changed nozzle types and spray quality respectively during the season. Sixty-two percent of the area was treated using flat fans, 30 % angled nozzles, 3% airassisted and 4% twin fluid. The use of angled nozzles increased from 22% of area at rosette stage to 33% for rapid haulm growth and 35% for full canopy. These nozzles generally replaced flat fans. Most of the area was treated with a medium spray quality (84%) and 12% with a fine spray. Coarse sprays, at 4%, were only recorded for full canopy and senescence. 3 British Potato Council 4

Sixty percent of growers changed their water volume for one of the four main growth stages. The most popular water volume at all four growth stages was 151 to l/ha (average of 50% by area), although 201 to 250 litres was as common at full canopy. The area treated with more than l/ha increased considerably after the rosette stage (17% at rosette, 29% at rapid haulm growth, 49% at full canopy and 44% at senescence). The use of less than 150 l/ha declined after rosette stage. The main reasons for growers changing how fungicide was applied to the crop are given below. Note that many respondents gave several reasons and therefore the percentage values by area do not add up to 100%. Growth stage 48% LERAP 27% Tank mixing 15% Spraying conditions 53% Fungicide choice 24% Crop assurance (not given) Time pressure 28% Watercourses 19% The results from the survey can be viewed in full in the blight section of the BPC website at www.potato.org.uk/blight in the report: Blight fungicide application grower survey 4. 2. Coverage demonstration (SAC at Potatoes in Practice sponsored by BPC and Syngenta) This non-replicated demonstration assessed six spray nozzles and water volumes. A contact acting plant desiccant, 4 litres of Reglone/ha, was sprayed on to plots of Cara to provide a visual demonstration of the penetration of a spray into a canopy and the coverage achieved for the different treatments. All treatments were sprayed at 3 bar pressure except the Billericay bubblejet which was applied at 2 bar. Eight randomly selected stems per plot were assessed 2 days after the diquat had been applied in early August 4. For each stem two leaves were assessed at each of the three positions (top, middle and bottom of the canopy). It is clear that no system of application gave good penetration/coverage of the lower leaves when the canopy was large (Fig.1). This demonstration provides a useful reminder that individual blight fungicide sprays applied when the haulm is large may not reach the majority of the canopy. Blight sprays applied in this way could put crops at risk from spores landing on lower leaves and stems. This emphasises the importance of building a robust fungicide programme from early in the growing season. British Potato Council 4 4

Figure 1 Blight fungicide application demonstration percentage coverage of leaf surface Nozzles Lurmark 01 F110 Lurmark 01 F110 Lurmark 02 F110 Lurmark 02 F110 Billericay Bubblejet Lilac 0.25 Syngenta Potato Nozzle Water volume (l/ha) Top leaves Middle leaves Bottom leaves 100 75.6 13.2 2.7 81.9 11.8 4.0 300 96.3 27.0 6.7 400 73.8 19.1 9.7 67.5 26.6 6.4 96.2 23.8 16.4 % coverage of leaf surface 120 100 80 60 40 20 0 Top leaves Middle leaves Bottom leaves Lurmark 01 F110 (100 l/ha) Lurmark 01 F110 ( l/ha) Lurmark 02 F110 (300 l/ha) Lurmark 02 F110 (400 l/ha) Billericay Bubblejet Syngenta Potato Nozzle ( l/ha) 3. Coverage demonstration (HAUC sponsored by BPC) A series of treatments to compare the effectiveness of different application strategies was developed. The treatments covered from low to high volume of water and with different nozzle types that produce a different droplet size and spray pattern. Rates and nozzle types are very much open to debate, depending on the amount of foliage, desired target, blight pressure, equipment available and environmental conditions. The objective of the demonstration was to stimulate debate in this area rather than provide definitive answers. To demonstrate the distribution pattern of the droplets from each nozzle, the desiccant Reglone was used as a marker to burn off the leaves that had been covered with the spray. In addition water sensitive paper was positioned at the top and 40 cm below the top of the canopy. Crop - Maris Piper planted 5 th May 4 Reglone rate - 3 litres per hectare Pressure - 3 Bar Sprayer used - Hardi 24m trailed sprayer with twin force air assistance. Plant samples were taken from each plot, 1 week and again 2 weeks after spraying. The plants were assessed for their green leaf area using a leaf area meter. The trial was a demonstration and not replicated so there isn t the advantage of statistical analysis to help conclusions to be drawn. It should also be noted that the results are for one application timing under one set of spraying conditions. 5 British Potato Council 4

The values in Fig. 2 represent percentage green leaf area remaining. The lower the number the more effective the application system. All the treatments had an immediate effect on green leaf area, some reducing green leaf area and keeping it suppressed where some reduced it to start with but then it increased in week two. The increase in green leaf area is due to re-growth of the plants, mainly from the growing tips of the new shots at the top of the canopy and development of the leaves that had not been covered by the spray. The green leaf area during the first week after sampling is more relevant to an assessment of coverage and penetration as this represents the coverage of the crop without the effects of re-growth. Figure 2 Percentage green leaf area remaining one week after application of diquat 30% 25% 20% 15% 10% 5% 0% Percent green leaf area remaining No air Air assisted 100 l/ha Air inclusion 02 Nozzle 100l/ha Flat Fan 02 Nozzle 400 l/ha Flat Fan 04 Nozzle 400l/ha Air Inclusion 04 Nozzle l/ha Air Inclusion 04 Nozzle l/ha Flat Fan 04 Nozzle l/ha Syngenta Potato Nozzle l/ha Twincap with 02 Flat Fan and 02 Air inclusion For l/ha the green leaf area value achieved with flat fans was slightly smaller than that obtained when air assistance was added or the air inclusion nozzle or Syngenta potato nozzle was used. The green leaf area results do not reflect the coverage demonstrated on water sensitive paper (Fig. 3). The water sensitive paper results suggest that air assistance should have improved, and the air inclusion nozzle should have made worse, the coverage and penetration of the diquat. At this water volume air assistance generally improved coverage of the paper at both heights in the canopy. The air inclusion nozzle produced too coarse a spray to give good coverage. Applying l/ha through the flat fans gave a lower green leaf value than 100 or 400 l/ha applied through flat fans. The water sensitive paper results confirm this result for 100 l/ha where coverage of the top of the canopy was limited due to the spray being British Potato Council 4 6

fine (Fig. 3). The penetration of this spray into dense inter-row foliage was very limited. Increasing the water volume to 400 l/ha for flat fans gave very good coverage of the top of the canopy but coverage of the lower canopy was inconsistent, with the dense foliage between rows proving difficult to cover. Figure 3 Spray coverage shown by water sensitive paper placed in crop canopy. (S Cooper and M Rodenhurst July 4) The most effective treatment within the trial was the flat fan nozzle with air assistance at 400l/ha. This was mainly due to the fact that any excess spray that wasn t intercepted by the leaves at the top of the canopy was forced downwards into the crop by the air assistance. However, switching to 400l/ha for blight spraying would often be impractical on most farms where a tight spray programme is followed and sprayers are working hard. 7 British Potato Council 4

4. Blight Fungicide Application Systems Trial (SAC at Auchincruive sponsored by BPC) A replicated trial, with four replicates, that compared applications of the contact fungicide mancozeb (1.7 kg product /ha) applied using different water volumes and nozzles was carried out. Treatments and spray dates are given in Table 1. Spray pressure was 3 bar for T1 to T4 but 2 bar where the air induction bubblejet nozzles () were used. The cultivar was King Edward. Table 1 Spray dates Ground cover (%, date assessed) 25 June 5 July 15 July 28 July 5 Aug 14 Aug 24 Aug 2 Sep 9 Sep 30, 91, 100, 100, 100, 93, - - - 24 th 9 th 16 th 23 rd 2 nd 16 th Growth stage 312 414 420 430 440 540 - - - T1 (F110-03) T2 (F110-03) 300 300 300 300 300 300 T3 (F110-03) 150 150 150 150 150 150 T4 (F110-03) 150 300 300 300 T5 Lilac 0.25 F110 03 F110 03 Spray interval - 10 10 13 8 9 10 9 7 F110 03 NB: All plots were treated with treatment 1 on 14 August because there was not enough of a spray window to apply the different treatments. By September there was so little green leaf left, less than 20% for most treatments, that there was no justification in applying the different treatments and all plots were again sprayed with treatment 1. The structure of the canopy was lost after exceptionally high rainfall on 8 to 10 August (> 100 mm). Many of the lower, older leaves were lost due to this rain. A detailed assessment of leaf and stem blight at different positions in the canopy was made starting on 18 August. The severity of blight on the bottom half of stems was significantly greater for 300 l/ha and the than the other systems (Table 2). For the upper stems differences between treatments were very small. The results for leaf blight were similar but differences were not significant even though 150 leaflets per plot were assessed at the two positions. British Potato Council 4 8

Table 2 Severity (%) of stem and leaflet infection on the top and bottom halves of the canopy in relation to the method used to apply 1.7 kg/ha mancozeb Nozzle Water volume (l/ha) % stem blight, top half % stem blight, bottom half % leaf infection, top % leaf infection, middle to bottom 03 F110 0.5 0.5 2.9 13.2 03 F110 300 0.5 2.4 7.1 26.5 03 F110 150 0.3 0.1 2.2 8.1 03 F110 Managed 0.4 0.2 1.8 10.7 Lilac 0.25 150 to 300 0.5 1.6 5.7 29.2 F pr. <0.001 0.420 0.182 LSD (P=0.05) 1.04 6.73 22.93 Results from 40 randomly selected stems per treatment 9 British Potato Council 4

Whole plot assessments of foliar blight were made during the growing season. Treatment differences were only significant on 19 August, not at later assessments. On the 19 th the severity of foliar blight was significantly worse for the 300 l/ha treatment than all treatments except (Fig. 4). Figure 4 Severity (%) of foliar blight (whole plot score) in relation to the method used to apply 1.7 kg/ha mancozeb Nozzle Water volume (l/ha) 19 Aug 26 Aug 2 Sep 9 Sep 03 F110 0.60 65.0 82.5 95.0 03 F110 300 0.80 65.0 88.1 95.6 03 F110 150 0.48 55.0 81.9 93.8 03 F110 Lilac 0.25 Managed 150 to 300 0.55 43.8 68.8 91.3 0.65 65.5 84.3 95.8 F pr. 0.029 0.463 0.232 0.397 LSD (P=0.05) 0.181 27.52 17.46 5.57 Severity of foliar blight (%) 120 100 80 60 40 20 03 F110 ( l/ha) 03 F110 (300 l/ha) 03 F110 (150 l/ha) 03 F110 (Managed 150-300 l/ha) Lilac 0.25 ( l/ha) 0 19.Aug 26.Aug 02.Sep 09.Sep Date of assessment British Potato Council 4 10

There were no significant differences in tuber blight control (Fig. 5). The much poorer control of tuber blight for the 150 l/ha system is a cause for concern but the reason for it is not clear. There were no significant differences in yield or blight-free yield (data not presented). Figure 5 Incidence (%) of pre-storage and total (pre-storage + poststorage) tuber blight in relation to the method used to apply 1.7 kg/ha mancozeb Nozzle Water volume (l/ha) Pre-storage Tuber blight Total Tuber blight 03 F110 11.8 25.2 03 F110 300 11.4 24.5 03 F110 150 23.7 35.1 03 F110 Lilac 0.25 Managed 150 to 300 11.6 20.7 14.4 24.0 F pr. 0.217 0.470 LSD (P=0.05) 12.23 15.16 Incidence of tuber blight (%) 40 35 30 25 20 15 10 5 03 F110 ( l/ha) 03 F110 (300 l/ha) 03 F110 (150 l/ha) 03 F110 (Managed 150-300 l/ha) Lilac 0.25 ( l/ha) 0 Pre-storage tuber blight Total tuber blight 11 British Potato Council 4

Conclusions and discussion Individual sprays applied to large haulm cannot give complete protection of the haulm. Fungicide control later in the season depends on enough fungicide protection having been built up lower in the canopy from the start of the programme. In 4 the managed water volume programme consistently gave the best control of leaf, stem and tuber blight. In an earlier trial in 1995 a similar regime matching water volume to canopy size, but using 0.3 l/ha of Shirlan (fluazinam), also gave the best control compared with fixed water volumes of 100, and 300 l/ha. The managed programme gave consistently good control in two very different seasons. In 1995 the blight risk was low until very late in the season with the first Smith Period being recorded on the 28 and 29 of August (Fig. 6). In contrast high-risk conditions occurred much earlier in 4 and were more prevalent. Figure 6 Smith Periods (SP) and foliar blight development in 4 compared with 1995 100 90 80 70 60 50 40 30 20 10 0 01.Jun 08.Jun15.Jun 22.Jun 29.Jun 06.Jul 13.Jul 20.Jul 27.Jul 03.Aug 10.Aug 17.Aug 24.Aug DATE % blight 4 % blight 1995 SP 4 31.Aug SP 1995 07.Sep 14.Sep One advantage of using smaller water volumes when the crop is small is that plants are treated with a higher concentration of fungicide (Table 3). In addition, there is less likely to be run-off of spray and loss of fungicide to the soil. The benefits of higher water volumes are only obtained when the haulm is large and it is important for spray to penetrate further into the canopy. British Potato Council 4 12

Table 3 Concentration of mancozeb solution for 1.7 kg/ha applied in different water volumes Water volume Concentration of mancozeb per (l/ha) litre of spray solution 150 11.3 8.5 300 5.7 Some treatments were not consistent in the two years. For example, the fixed 300 l/ha gave poor control of foliar blight in 4 and yet gave very good control in 1995. This inconsistency is most easily explained by the timing of blight risk in the two years. In 4 the plants were challenged early. Those treated with mancozeb in 300 l/ha were treated with a more dilute fungicide solution but were challenged before the benefits of the larger volume occurred. In contrast the much later challenge in 5 occurred after the benefits of the larger water volume had been obtained. However, it must be remembered that there were other differences between the trials that could have influenced the results. The influence of the different fungicides, fluazinam compared with mancozeb, and the fact that the canopy structure was severely impaired by exceptional rainfall in 4 must also be considered. The poor canopy structure after 10 August reduced the advantage of later applications in larger water volumes. In both 4 and 1995 the managed water volume programme gave better control of foliar and tuber blight than the fixed l/ha. The low drift, air induction nozzles in the 4 trial gave poor control of blight. This was most likely because the spray quality was too coarse to give good coverage. Low drift nozzles should be kept for the situation when not to use them would lead to a spray timing being missed. It is important to remember that fungicide timing is critical and it is generally better to apply a fungicide less perfectly than extend an interval. In addition the poor spray coverage can be compensated for to some extent when the next spray is applied. There is no obvious explanation for the fixed rate of 150 l/ha in 4 giving very good control of foliar blight but poor control of tuber blight. British Potato Council, 4300 Nash Court, John Smith Drive, Oxford Business Park, Oxford, OX4 2RT