About Powdery Mildew:

Cal-Agri Plant Foliar Treatments

Powdery Mildew on Strawberry and Oilseed Rape Plants

Powdery mildews are probably the most serious of plant fungal diseases and affect both outdoor and protected plants. A number of different powdery mildew species exist although all are Ascomycete fungi belonging to the Erysiphe family. It is normally important that the species of powdery mildew infecting a plant is identified so that a suitable chemical product can be used to control it. For the studies listed below, the resources were not available to accurately identify the different species of powdery mildew, so it had to be assumed that the infections were typically the species that affected the specific host plant species.

TREATMENT STUDIES:  Strawberry   |  Oilseed Rape 1  |  Oilseed Rape 2

Evaluation of Preventative and Curative effects
of Agri-Colle on Powdery Mildew Infections

An independent study undertaken in the United Kingdom, January 2006

Aim of Study:
To determine the effects of regular applications of 1.5ml/l Agri-Colle at preventing or controlling infestations of powdery mildews (Ascomycete fungi) under controlled conditions.

Background information relevant to this study:
In the case of the strawberry plants, the powdery mildew was assumed to be: Strawberry Powdery Mildew (Sphaerotheca macularis)

The oilseed rape plants were likely to have been infested with
Brassica Powdery Mildew (Erysiphe cruciferarum).

It was also decided that accurate identification of the Powdery Mildew species was not entirely relevant in evaluating Agri-Colle, since its mode of action was assumed to be by a physical means. If this was the case, then the effects of Agri-Colle should be assumed generic for all Powdery Mildew-like fungal infections.

Despite this assumption, it was possible that Agri-Colle produced different effects when used to prevent plants from becoming infected with powdery mildews (ie. Prophylactic application) or for controlling powdery mildews on already infected plants (ie. Curative application).

Suitable locations and target plants were therefore selected to
undertake the two evaluations.

^TOP EVALUATION 1:
Agri-Colle applied as a curative treatment for
Powdery Mildew on Strawberry plants

Materials and Methods:
A commercial strawberry grower allowed a small evaluation to be undertaken on plants infested with powdery mildew. The plants were growing in a glasshouse within a suspended trough system. Plants were irrigated and fed through drippers into the compost and were heated from below from piped hot water. On average 5 or 6 strawberry plants were growing per 0.5m long trough.

Eight consecutive troughs were provided for testing.

Four troughs were sprayed to run-off point with a 1.5ml/l dilution of Agri-Colle.
Four troughs were sprayed to run-off point with a 1.0ml/l dilution of Agri-Colle.

Tap water was used for both dilutions and the treatments were applied
using a medium droplet hand held sprayer.

Volumes were estimated to be equivalent to 2000 litres per hectare.

Treated plants were to be compared to untreated plants in
troughs either side of the treated rows.

Only 2 applications of Agri-Colle, seven days apart, could be applied
to the test plants as the glasshouse had to be cleared for a new crop.

These applications were made on 25.11.05 and on 02.12.05.

All plants within the evaluation had visible areas of mildew on their leaves prior to treatment (Fig. 1). However, ten infested leaves were tagged to ensure they could be studied in more detail at the end of the evaluation.

Seven days after the second application (09.12.05), the treated plants were assessed and compared to untreated plants. The effectiveness of the treatments was determined by any noticeable reduction in the level of powdery mildew infection on the treated plants in relation to the untreated plants.

Figure 1: Strawberry leaf infested with powdery mildew
prior to treatment with Agri-Colle.

Results
Fourteen days after the first application of Agri-Colle (seven days after the second application), a clear difference could be seen between plants within the different treatments.

Plants that had been treated with Agri-Colle at 1.5ml/l had greatly reduced levels of powdery mildew infestation. Seven of the ten tagged infested leaves appeared clear of powdery mildew although a light coloured stain was visible where fungal growth had been present. Low levels of mildew were still present on the three remaining tagged leaves.

Plants treated with Agri-Colle at 1.0ml/l exhibited less mildew than on the untreated plants, although considerably more than on the plants treated with the 1.5ml/l application.

The results from this study demonstrated a clear difference in the level of powdery mildew infestation on strawberry plants treated with 1.5ml/l Agri-Colle to those left untreated. However, other areas close to the trial had been treated with foliar applications of a systemic myclobutanil-based fungicide. Since it cannot be ruled out that spray drift may have affected this trial a further investigation has to be undertaken.

^TOP EVALUATION 2:
Agri-Colle applied as a preventative treatment for
Powdery Mildew on oilseed rape plants

Materials and Methods:
Oilseed rape plants (Brassica napus) were grown on a regular basis within a heated and lit glasshouse for cross pollination studies. The plants within this glasshouse were prone to mildew and would normally have been regularly treated with sulphur. However, the location provided an ideal opportunity to investigate the potential of Agri-Colle for protecting plants from mildew.

Twelve young oilseed rape plants were selected for this study. All plants were free from mildew and none of the plants had been treated with any preventative mildewcides.

The plants were separated into two groups of six plants. At weekly intervals, one group of plants was sprayed with water. The other group of plants was sprayed with 1.5ml/l Agri-Colle. The treatments were applied to run off point on both upper and lower leaf surfaces.

Plants were checked for the appearance of mildew
prior to each new application.

Results:
The first application of Agri-Colle was made on 1/12/05. However, it wasn't until the fifth application was due on 29/12/05, that mildew first began appearing on plants within the water control treatment. No mildew could be found on any of the Agri-Colle treated plants (Figs 2 and 3).

Treatments continued at weekly intervals until 17/01/06 when a clear difference between the water treated controls and the Agri-Colle
treated plants could be seen.

Mildew had become established on the water treated control plants (Fig. 4) and was even appearing on the seed pods (Fig. 5). The Agri-Colle treated plants remained clear from mildew (Fig 6).

Concluding Comments:
This study has provided strong evidence that regular and thorough applications of 1.5ml/l Agri-Colle can help to prevent mildew from becoming established on susceptible plants such as oilseed rape under the conditions used for this study.

Figure 2: Mildew appearing on oilseed rape plants within the water treated control

Figure 3: Plants treated with four weekly applications of 1.5ml/l Agri-Colle,
displaying no signs of mildew

Figure 4: Established mildew on a water treated oilseed rape plant

Figure 5: Mildew affecting a seed pod of a water treated oilseed rape plant

Figure 6: Oilseed rape plants remained free of mildew after
7 weekly applications of 1.5ml/l Agri-Colle.

^TOP EVALUATION 3:
Agri-Colle applied as a curative treatment for
Powdery Mildew on Oilseed Rape plants

Evaluation 1 did not provide a clear indication as to whether Agri-Colle can effectively be used as a curative treatment for Powdery Mildew on commercial strawberry plants. The grower was not able to ensure that this study could be repeated within the commercial environment without the possibility of essential treatments for pests and diseases being applied as and when necessary. It was therefore decided to postpone any further studies until the crop became seasonal and therefore less valuable. In the interim period, the mildew infected oilseed rape plants from the water treated controls of Evaluation 2 were selected for use in Evaluation 3.

Materials and Methods:
The six oilseed rape plants from the water treated control of Evaluation 2
were separated into two groups of three plants.

One group of plants was sprayed with water. The other group of plants was sprayed with 1.5ml/l Agri-Colle. The treatments were applied to run off point on both upper and lower leaf surfaces. This was repeated 3 times at 3 day intervals before the plants were assessed for the level of mildew.

Results:
Powdery mildew could clearly be seen within the effluent that ran off the leaves after treatment with 1.5ml/l Agri-Colle. The leaves then appeared clean whilst the treatment air dried. (Fig. 7.). However, when the leaves had dried, the mildew infection was still evident.

After the third application, the water treated control plants remained heavily infected with mildew, whereas the Agri-Colle treated plants were less affected. In addition, the mildew on the Agri-Colle treated plants did not appear 'powdery' but instead had become more glutinous in appearance (Fig.8).

Figure 7: A mildew infested oilseed rape leaf before (top) and
immediately after treatment with 1.5ml/l Agri-Colle (bottom)

Figure 8: Oilseed rape leaf after 3 treatments of 1.5ml/l Agri-Colle at
3 day intervals. Although still visible, the mildew no longer appears 'powdery'.

^TOP Concluding comments:
These studies have demonstrated that weekly applications of 1.5ml/l Agri-Colle, sprayed to run-off point on oilseed rape plants can protect the plants from becoming infected with powdery mildew under the conditions used for this work. Water treated plants that were grown alongside the Agri-Colle treated plants all became infected with powdery mildew whereas no powdery mildew was found on any of the Agri-Colle treated plants.

When 1.5ml/l Agri-Colle was sprayed on to oilseed rape plants already infected with powdery mildew at 3 day intervals, a clear reduction in the level of infection was apparent. The powdery mildew also appeared not to be sporulating and had lost its 'powdery' appearance.

These studies have clearly demonstrated the potential of Agri-Colle for use as an effective mildewcide. Further studies within a commercial growing environment will follow this study.

No evidence of phytotoxicity was seen during these studies.