Potatoes..spray for blight or not?

loopy · Rank attained: Hazel Tree Joined: 10 Jul 2006 Posts: 43

Given the warm damp conditions forecast, should we be spraying for potato blight this week or not? Havent seen anything about it and was wondering this. I assume its too late once the leaves have gone brown?

My potatotes are doing great (in growing bags) and look dark green and healthy, however some leaves have been munched (edges gone). Should I be spraying anything for this?

Normally I like to garden as organically as possible so any organic friendly spray recommendations would be great for both the above! thanks

michael brenock · Posted: Tue May 19, 2009 7:45 pm Post subject:

have not seen or experienced any blight yet, too cold for it. dont know what damage is at edge of leaf a picture would help, maybe slugs, the browning might be due to early frost cold winds or normal senescence. there is no need to spray for every symptom that appears, potatoes are normally hardy
Wait for a blight warning and grow the varieties that are more resistant to blight.
michael brenock horticultural advisor (retired)

Fiachra · Rank attained: Hazel Tree Joined: 04 Jan 2009 Posts: 31

I was wondering about blight myself.This is my first time growing spuds so I was a bit unsure whether to spray or not. I have put out beer traps for the slugs as the edges of some of the leaves have been eaten too.
I have also planted some kerrs pinks and sarpo axonos about three weeks ago. they had been chitted. I am a bit worried that only two out of about 60 are peeping through.I mixed in lots of horse manure with the soil - am I after killing them?

Liparis · Posted: Wed May 20, 2009 8:53 am Post subject:

I wouldn't worry yet. There are several factors that may be involved in the time of potatoes making an appearance; soil temperature, depth of planting etc. One day you will look out and find all your spuds standing in a row. Horse manure is one of the very few manures you can put in with your crop, although you might get scab from it, but not as bad, but it's unlikely to kill your potatoes.
Bill.

loopy · Rank attained: Hazel Tree Joined: 10 Jul 2006 Posts: 43

Thanks everyone, I was worried in case i went out and all were gone! I did find one very fat slug in one of the bags this morning, only the one and although leaf damage is done, he doesnt seem to have attacked the potato stems, will these be ok do you think? Dont even know how the slugs got in..I have the potato bags on a bench, its some distance for them to slither up!! Laughing

Is it ok to add slug pellets in the bag itself?

Belfast · Posted: Wed May 20, 2009 4:59 pm Post subject:

sarpo axona are blight resistant
Sarpo Axona - late maincrop

kerr pinks are not blight resistant
Early Main Crop

I found my sarpo axona a bit slow to grow compared to the other spuds (British Queens) that I am growing this year.

Keep an eye out for Slugs in this wet weather.

michael brenock · Posted: Wed May 20, 2009 9:21 pm Post subject:

common scab is encouraged by high pH or too much lime in the soil. Farmyard manure or cow manure is suitable for growing potatoes, however fresh horse manure contains a lot of ammonia and may retard growth for a while before giving a boost to leaf growth which is not desirable.
michael brenock horticultural advisor (retired)

Liparis · Posted: Wed May 20, 2009 11:20 pm Post subject:

I need to dispute that, Michael, sorry. If you mean fresh horse manure straight from the horses botty, then that may well be correct. However the term fresh for any manure is manure taken from a stable, stacked and then used the same season. While Ammonia content is high in horse manure it volatizes at speed of somewhere around 4 times that of cow manure. Within 24 hrs it has volatized to between 50% and 60% of it's original level. While cattle manure is lower, it volatizes much slower. This is caused by compaction.
Cattle are kept on deep litter, nothing is taken away but sufficient straw is added daily to keep them on dry bedding, this assists in providing heat. The Ammonia is trapped inside by the compaction of the cattle. This doesn't happen with horse manure unless your husbandry is appallingly poor. Solids and wet bedding, usually wood chips or sawdust or wood pellets are removed from the stable twice daily. The result is very low Ammonia in the dung heap and rapid volatizing because their is practically no compaction. Horse are very respiratory sensitive to Ammonia, hence the removal of soiled bedding twice per day.
If horse manure is used fresh, ie straight from the orifice, it is only ever used as a top dressing, no Ammonia is trapped in the ground it all volatizes. But if it used fresh as in the usual sense, ie the same season the stack is made, then it has extremely low levels of ammonia, much lower than cattle manure of the same age. It's so beneficial to plants of all types that horse trails are great places, much better than a cattle field, to go looking for wild plants and flowers. Horse fields are also higher in wild flower populations.
Bill.

Sean Ph'lib · Posted: Thu May 21, 2009 7:58 am Post subject:

I agree. I always use horse manure in my garden, whenever I can get it. If it's last year's it goes on as is; this year's goes into the compost bin. It's great stuff!

Michael196 · Posted: Thu May 21, 2009 8:37 am Post subject:

Dithane 945 Blight Control

When to apply:

Spray before crop is infected with blight.

Apply first spray before haulm meets across the rows. Repeat spraying every 10-14 days.

Under fast plant growth and prolonged blight conditions, reduce spray interval to 5-7 days.

loopy · Rank attained: Hazel Tree Joined: 10 Jul 2006 Posts: 43

Michael196 · Posted: Thu May 21, 2009 12:31 pm Post subject:

there is no direct reference to a tim however the Royal horticultural society people suggest June onwards :

http://www.rhs.org.uk/advicesearch/profile.aspx?PID=217

I guess the size of the potatoe haulm ( plant) indicates when blight may be near .

check out Met eireann who can tell you when blight is likely to be around

http://www.met.ie/forecasts/warnings.asp

As regards your pics, I realy would not be worried about such small damage.

I think I would remove the slug pellets. remember the same soil is feeding your future food, so dont contaminate your potatoes food. Just pick them off and leave them for the birds.

When your stalks are in flower, water generoulsy without overdoing it , as this is when the potatoes are forming.

the stalk will die back naturally to the point of decomposing on the ground but your potatoes undergoround will be be thriving.

think of the process of storing the potatoes.

michael brenock · Posted: Thu May 21, 2009 12:33 pm Post subject:

bill i thanks for your comment I stand corrected in that I should have explained what is meant by fresh manure. i know little or nothing about horses or their trails or how good their trails are for growing vegetables. i am always anxious to learn more about any topic of gardening even if it means learning about horses. I am very conscious of the beneficial effects of stable manure to the physical qualities of the soil.
michael brenock horticultural advisor (retired)

loopy · Rank attained: Hazel Tree Joined: 10 Jul 2006 Posts: 43

Michael196 · Posted: Thu May 21, 2009 12:51 pm Post subject: Dithane 945

I recommedn Dithane for your blight spraying.

Dithane is a sporicide. Blight is a mould that reproduces by forming spores, which become airbourne and therefore can travel. Perhaps this is why the dithane can says to spray before the haulms touch, as touch contact may be the first vehicle of spreading.

Remeber to spray underneath the leaves also. There is also a growth affetc to the sporicide when sprayed.

Think of sporicides as disinfectants, like your dettol spray etc, Sporicides are killing the airborne bacterias ( spores) that form disease ( mould- blight).

I bought a hozelock sprayer 2 years ago to spray potatoes , everything worked fine. Some stalks did submit to blight , towards the end of the season, ( august september), but the potatoes themselves were fine.