Tillage Update May 28th
Type Media Article
Included in this weeks update is the Virtual Crop walk, the variation in spring crops due to rainfall variation, spring beans, grass weeds and the mangold fly in fodder beet,
Variation in spring crops
There are large variations in growth stages and crop density in spring crops this season due to varied rainfall amounts. All crops are in need of moisture but crops in the north east are more severely affected. Spring crops need to be managed differently depending on crop density and amount of recent rain.
Crops along the south coast have fared best where 140mm of rain has been recorded at Cork airport since April 1st compared to crops in the north east where only 23mm of rain has been recorded at Dublin airport.
While spring bean crops are in need of moisture it is still important to be vigilant of disease. Disease levels are likely to remain low in the absence of rain but there have been reports of chocolate spot in Cork and downy mildew in Wicklow.
Preventative sprays are best for chocolate spot so apply a fungicide at start of flowering and repeat 2-3 weeks later if conditions are conducive to disease.
Options include: Signum 0.5-0.75 kg/ha or Amistar 0.5 L/ha + Tebuconazole 0.75 L/ha
Ridomil Gold offers some curative control of downy mildew as it contains metlyaxyl. Basfoliar Aktiv and Nutriphite PGA are bio-stimulants and claim improved plant resistance against downy mildew so can be useful where it is expected.
In this video Jimmy Staples emphasise the importance of Integrated Pest Management (IPM) strategies in the control of grass weeds. IPM starts with correct weed identification and understanding the weed biology.
Preventing seed return is the focus at this time of year so it is important to remove weeds before they shed seed. One blackgrass plant/m² can produce 10,000 seeds or 6 million seeds/ha. Where infestations are low hand rogueing is very effective but where there are high weed infestations whole cropping or crop destruction may be required to prevent seed return.
We have an on-going survey to help inform us and the industry about the level of grass weeds and grass weed herbicide resistance in the country at the moment please click on the link and fill out the survey it should only take about 10 to 15 minutes
The larvae of the mangold fly has been observed in many fodder beet crops in recent days. The most common damage is the feeding between the upper and lower leaf surfaces of seedling beet plants by the larvae. The damage resembles a blistering of the leaf in which the larvae can be found.
Control options are limited and success depends on very precise timings. It is important to ensure that the threshold is exceeded before insecticide application as insecticide application can be harmful to beneficial insects.
Figure 1. Leaf miner
The threshold for treatment is when the number of eggs and larvae exceeds the square of the number of true leaves.
For example, a plant with six true leaves would need a population of 36 or more eggs and larvae to warrant treatment. A crop with 10 true leaves would need a population of 100 or more eggs and larvae. The underside of leaves is the best place to look for eggs and larvae to determine pest numbers.
Figure 2: Mangold fly eggs are white, patterned and about 1mm long. Picture from Cork on May 25th 2020.
Contact insecticides will only have limited control of leaf miner. A BBRO-funded project carried out by ADAS in 2015 to investigate alternative chemical control options for mangold fly found that the most effective control was achieved when the contact insecticide Karate Zeon treatments were applied at egg-laying and, particularly, egg-hatch.
Karate Zeon and DecisProtech are approved in Ireland and are contact insecticides. Therefore applications need to be timed accurately to strike the larvae before they enter the leaves. Otherwise the larvae will be protected by the leaf epidermis and control can be limited. Tefluthrin (Force) is the most common seed treatment used this season for soil pest control, but this product does not control leaf miner.
Insecticides should only be applied when thresholds are exceeded and need to be targeted before the larvae enters the leaf otherwise they will have a negative impact on beneficial insects.
Virtual Crop walk
Teagasc will hold its second LIVE Virtual Crop walk on Thursday May 28th at 6:30 -7:30pm and we are encouraging farmers to join in and ask questions.
Building on the success of the last Virtual Crop walk this event will have feeds from Cork, Wexford and Meath.
A panel in the studio (Stephen Kildea, Shay Phelan and Jimmy Staples) will discuss these regional differences and how farmers can best manage crops in their area.
The Virtual Crop walk will discuss
- Spring Crops (barley, wheat, oats and beans)
- Grass weeds on tillage farms